As filed with the Securities and Exchange Commission on October 18, 2005

Registration No. 333-            

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form S-4

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Mariner Energy, Inc.

(Exact name of registrant as specified in its charter)

2101 CityWest Blvd., Bldg. 4, Suite 900

Houston, Texas 77042

(713) 954-5500

(Address, including zip code, and telephone number,

including area code, of registrant’s principal executive offices)

Teresa Bushman

Vice President and General Counsel

Mariner Energy, Inc.

2101 CityWest Blvd., Bldg. 4, Suite 900

Houston, Texas 77042

(713) 954-5505

(Name, address, including zip code, and telephone number,

including area code, of agent for service)

Copies to:

      Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this registration statement becomes effective and upon consummation of the merger described in the enclosed proxy statement/ prospectus-information statement.

      If the securities being registered on this Form are to be offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box.     o

      If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act of 1933, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.     o

      If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act of 1933, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.     o

      The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

SUBJECT TO COMPLETION DATED OCTOBER 18, 2005

Houston, Texas

                    , 2005

Fellow Stockholder:

      We invite you to attend a special meeting of stockholders of Mariner Energy, Inc. to be held on                     ,                     , 2005 at 10:00 a.m., Central Standard Time, at                                                                   , Houston, Texas             . At the special meeting, you will be asked to consider and vote upon a proposal to adopt the merger agreement entered into among Mariner, Forest Oil Corporation, Forest Energy Resources, Inc. and MEI Sub, Inc., to consider and vote upon a proposal to amend Mariner’s certificate of incorporation to increase its authorized shares of stock, and to consider and vote upon a proposed amendment and restatement of Mariner’s stock incentive plan.

      If the merger agreement is adopted and the merger consummated, Forest Energy Resources will become a wholly owned subsidiary of Mariner, and Mariner will be a publicly traded company. Mariner will apply to list its common stock on the New York Stock Exchange. Each Forest shareholder will be entitled to receive one share of common stock of Mariner in exchange for each share of Forest Energy Resources common stock they own. Mariner stockholders will not receive consideration in the merger.

      We believe that this transaction will increase Mariner’s scale and balance its portfolio in the Gulf of Mexico, provide a strong financial platform for our exploration and development efforts, and enlarge our stockholder base for greater liquidity. There are, however, risks associated with the proposed transaction, some of which are described under “Risk Factors” beginning on page 14 of the accompanying proxy statement/ prospectus-information statement.

      The Mariner board of directors has determined that the merger is fair to and in the best interests of Mariner and its stockholders, and that the merger agreement is advisable. The Mariner board of directors has unanimously approved the merger agreement and recommends that the Mariner stockholders vote “for” the adoption of the merger agreement.

      In order to consummate the merger, Mariner’s certificate of incorporation must be amended to increase the number of shares of stock Mariner is authorized to issue. Mariner proposes to increase its authorized shares from 90 million, of which 70 million are shares of common stock and 20 million are shares of preferred stock, to 200 million, of which 180 million will be shares of common stock and 20 million will be shares of preferred stock, subject to the completion of the merger. The Mariner board of directors has unanimously approved the amendment to the certificate of incorporation, and recommends that the Mariner stockholders vote “for” the amendment.

      Mariner also proposes to amend and restate its stock incentive plan, whereby 4.5 million shares of common stock, or approximately 5% of its outstanding shares following the completion of the merger, would be added to the plan, subject to the completion of the merger. The restated plan would be extended to October 12, 2015 and would limit the number of shares subject to stock options or shares of restricted stock issuable under the plan to any individual to 2.85 million. The Mariner board of directors has unanimously approved the amended and restated stock incentive plan, and recommends that the Mariner stockholders vote “for” the amended and restated plan.

      All stockholders are invited to attend the special meeting. Your participation at the special meeting, in person or in proxy, is important. Even if you only own a few shares, we want your shares to be represented at the meeting. The merger cannot be completed without the approval of the holders of a majority of the outstanding shares of common stock of Mariner. Whether or not you expect to attend the special meeting in person, please complete, sign, date and promptly return the enclosed proxy card in the enclosed postage-prepaid envelope. Stockholders of record also have the option of voting via the Internet or by telephone. Specific instructions on how to vote via the Internet or by telephone are included on the proxy card. Each proxy is revocable and will not affect your right to vote in person if you attend the special meeting.

      The proxy statement/ prospectus-information statement that accompanies this letter contains detailed information about the proposed merger and the other proposals, and we urge you to read it carefully. In particular, you should read the “Risk Factors” section beginning on page 14 for a description of various risks you should consider in evaluating the proposed merger.

      Thank you and we look forward to seeing you at the meeting.

      Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved the new shares of Mariner common stock to be issued in the merger or determined that this proxy statement/ prospectus-information statement is accurate or complete. Any representation to the contrary is a criminal offense.

      This proxy statement/ prospectus-information statement is dated                     , 2005, and is first being mailed to stockholders on or about                     , 2005.

      This proxy statement/prospectus-information statement incorporates by reference important business and financial information about Mariner Energy, Inc. from documents that are not included in or delivered with this proxy statement/prospectus-information statement. This information is available to you without charge upon your written or oral request. You can obtain the documents incorporated by reference in this proxy statement/prospectus-information statement by requesting them in writing or by telephone from Mariner Energy, Inc. at the following address and telephone number:

Denver, Colorado

                    , 2005

To the Shareholders of Forest Oil Corporation:

      On September 12, 2005, we announced that we would spin-off to our shareholders our offshore Gulf of Mexico operations, and that the Gulf of Mexico operations would immediately thereafter be acquired in a merger transaction by Mariner Energy, Inc. After the spin-off and merger, Mariner will be a separately traded public company that will own and operate the combination of Mariner’s business and our Gulf of Mexico operations.

      As a result of the transaction, in addition to retaining all of your shares of Forest common stock, you will receive approximately 0.8 shares of Mariner common stock for each Forest share you own on the record date of the transaction. You will not be required to pay for the shares of Mariner common stock that you receive. Forest shareholders will receive approximately 58% of the common stock of Mariner on a pro forma basis. Mariner will apply to list its common stock on the New York Stock Exchange.

      This transaction represents a significant strategic step that we believe will sharpen Forest’s focus on its onshore businesses, and will provide operational clarity. While we believe the spin-off will also allow Forest shareholders to benefit from the success and upside potential of Mariner, there are risks that are described under “Risk Factors” beginning on page 14 of the accompanying proxy statement/ prospectus-information statement.

      Forest’s board of directors has determined that the spin-off of the Gulf of Mexico operations and the combination of these operations with Mariner are advisable and in the best interests of Forest and its shareholders, and has approved the proposed transaction. You need not take any action to participate in the spin-off or the merger — no vote of Forest shareholders is required in connection with this transaction. Following the completion of the merger, you will receive information explaining how to obtain your shares of Mariner common stock.

      The following document constitutes an information statement of Forest relating to the spin-off and contains important information describing the terms of the spin-off, the merger, Forest, Mariner, the Forest Gulf of Mexico operations and the combined businesses. We encourage you to read it carefully.

      We look forward to completing the spin-off and merger and to the exciting opportunities this transaction presents for our shareholders.

Houston, Texas

                    , 2005

Notice of Special Meeting of Stockholders

To the Stockholders of Mariner Energy, Inc.

      A special meeting of holders of common stock of Mariner Energy, Inc. will be held on                     ,                     , 2005 at 10:00 a.m., Central Standard Time, at                        , Houston, Texas             ,

      The board of directors of Mariner has determined that owners of record of Mariner’s common stock at the close of business on                     , 2005 are entitled to notice of, and have the right to vote at, the Mariner special meeting and any reconvened meeting following any adjournment or postponement of the meeting.

      The Mariner board of directors has determined that the merger is fair to and in the best interests of Mariner and its stockholders, and that the merger agreement is advisable. The Mariner board of directors has unanimously approved the merger agreement, the proposed amendment to Mariner’s certificate of incorporation and the proposed amendment and restatement of Mariner’s stock incentive plan, and recommends that the Mariner stockholders vote “for” the adoption of the merger agreement and the other proposals.

PROXY STATEMENT/ PROSPECTUS-INFORMATION STATEMENT

Table of Contents

QUESTIONS AND ANSWERS ABOUT THE MERGER

	•	a proxy statement of Mariner for use in the solicitation of proxies for Mariner’s special meeting of stockholders;
	•	a prospectus of Mariner relating to the issuance of shares of Mariner common stock in connection with the merger; and
	•	an information statement of Forest relating to the spin-off of the Forest Gulf of Mexico operations to the shareholders of Forest.

	•	The terms “we”, “us”, “our” and like terms, and the term “Mariner,” refer to Mariner Energy, Inc.;
	•	“MEI Sub” refers to MEI Sub, Inc.;
	•	“Forest” refers to Forest Oil Corporation;
	•	“Forest Energy Resources” refers to Forest Energy Resources, Inc.; and
	•	“Forest Gulf of Mexico operations” refers to the offshore Gulf of Mexico operations conducted by Forest that will be contributed to Forest Energy Resources and spun-off to Forest shareholders.

	•	be an independent public company;
	•	own both the Mariner operations and the Forest Gulf of Mexico operations; and
	•	have total assets of approximately $2.1 billion and total debt of approximately $299.0 million on a pro forma combined basis, assuming the spin-off and the merger occurred on June 30, 2005.

	•	the adoption of the merger agreement by Mariner stockholders holding a majority of the Mariner common stock and the approval of the proposed amendment to Mariner’s certificate of incorporation;
	•	the absence of legal restrictions that would prevent the completion of the transactions;
	•	the receipt by Forest, Mariner and Forest Energy Resources of an opinion from their respective counsel to the effect that the merger will be treated as a reorganization for federal income tax purposes;
	•	the completion of the spin-off in accordance with the distribution agreement;
	•	the receipt of material consents, approvals and authorizations of governmental authorities;
	•	the expiration or termination of any applicable waiting period under the Hart-Scott-Rodino Act;
	•	the SEC declaring effective the registration statements of Mariner relating to the shares of Mariner common stock to be issued in the merger and those shares held by its existing stockholders;
	•	the approval for listing on the New York Stock Exchange or Nasdaq of Mariner’s common stock; and
	•	Mariner and Forest receiving the consents required pursuant to their credit facilities, and Forest receiving the consents required from its bondholders.

	•	the other party breaches its representations, warranties, covenants or agreements under the merger agreement so as to create a material adverse effect, and the breach has not been cured within 30 days after notice was given of such breach;
	•	the parties do not complete the merger by March 31, 2006;
	•	a governmental order prohibits the merger; or
	•	Mariner does not receive the required approval of its stockholders.

	•	arrangements regarding the appointment of directors and officers of Mariner following the merger; and
	•	arrangements whereby the executive officers of Mariner will receive a cash payment of $1,000 each in exchange for the waiver of certain rights under their employment agreements, including the automatic vesting or acceleration of restricted stock and options upon the completion of the merger and the right to receive a lump sum cash payment if the officer voluntarily terminates employment without good reason within nine months following the completion of the merger.

				Post-2004 Merger													Pre-2004 Merger
								Period from				Period from					Period from
								March 3,				March 3,					January 1,
				Six Months				2004				2004					2004
				Ended				through				through					through				Year Ended December 31,
				June 30,				June 30,				December 31,					March 2,
				2005				2004				2004					2004				2003				2002				2001				2000
				(In millions, except per share data)
Statement of Operations Data:
	Total revenues(1)			$	107.6			$	72.3			$	174.4				$	39.8			$	142.5			$	158.2			$	155.0			$	121.1
	Lease operating expenses				13.2				9.7				21.4					4.1				24.7				26.1				20.1				17.2
	Transportation expenses				1.5				2.4				1.9					1.1				6.3				10.5				12.0				7.8
	Depreciation, depletion and amortization				31.1				21.2				54.3					10.6				48.3				70.8				63.5				56.8
	Impairment of production equipment held for use				—				—				1.0					—				—				—				—				—
	Derivative settlement				—				—				—					—				3.2				—				—				—
	Impairment of Enron related receivables				—				—				—					—				—				3.2				29.5				—
	General and administrative expenses				15.4				4.3				7.6					1.1				8.1				7.7				9.3				6.5
	Operating income				46.4				34.7				88.2					22.9				51.9				39.9				20.6				32.8
	Interest income				0.6				0.1				0.2					0.1				0.8				0.4				0.7				0.1
	Interest expense				(3.6	)			(2.7	)			(6.0	)				—				(7.0	)			(10.3	)			(8.9	)			(11.0	)
	Income before income taxes				43.4				32.1				82.4					23.0				45.7				30.0				12.4				21.9
	Provision for income taxes				(14.8	)			(10.7	)			(28.8	)				(8.1	)			(9.4	)			—				—				—
	Income before cumulative effect of change in accounting method net of tax effects				28.6				21.4				53.6					14.9				36.3				30.0				12.4				21.9
	Income before cumulative effect per common share
		Basic			0.90				0.72				1.80					.50				1.22				1.01				.42				.74
		Diluted			0.89				0.72				1.80					.50				1.22				1.01				.42				.74
	Cumulative effect of changes in accounting method				—				—				—					—				1.9				—				—				—
	Net income			$	28.6			$	21.4			$	53.6				$	14.9			$	38.2			$	30.0			$	12.4			$	21.9
	Net income per common share
		Basic			0.90				0.72				1.80					.50				1.29				1.01				.42				.74
		Diluted			0.89				0.72				1.80					.50				1.29				1.01				.42				.74
Capital Expenditure and Disposal Data:
	Exploration, including leasehold/seismic			$	7.5			$	17.6			$	40.4				$	7.5			$	31.6			$	40.4			$	66.3			$	46.7
	Development and other				72.0				18.7				93.2					7.8				51.7				65.7				98.2				61.4
	Proceeds from property conveyances				—				—				—					—				(121.6	)			(52.3	)			(90.5	)			(29.0	)
	Total capital expenditures net of proceeds from property conveyances			$	79.5			$	36.3			$	133.6				$	15.3			$	(38.3	)		$	53.8			$	74.0			$	79.1

			Post-2004 Merger									Pre-2004 Merger
												December 31,
			June 30,				December 31,
			2005				2004					2003				2002				2001				2000
			(In millions)
Balance Sheet Data:(1)
	Property and equipment, net, full cost method		$	351.3			$	303.8				$	207.9			$	287.6			$	290.6			$	287.8
	Total assets			463.1				376.0					312.1				360.2				363.9				335.4
	Long-term debt, less current maturities			99.0				115.0					—				99.8				99.8				129.7
	Stockholder’s equity			201.0				133.9					218.2				170.1				180.1				141.9
	Working capital (deficit)(2)			18.3				(18.7	)				38.3				(24.4	)			(19.6	)			(15.4	)

(1)	Balance sheet data as of December 31, 2004 reflects purchase accounting adjustments to oil and gas properties, total assets and stockholder’s equity resulting from the acquisition of our former indirect parent on March 2, 2004.
(2)	Working capital (deficit) excludes current derivative assets and liabilities, deferred tax assets and restricted cash.

		Post-2004 Merger													Pre-2004 Merger
										Period from					Period from
						Period from				March 3,					January 1,
		Six Months				March 3,				2004					2004
		Ended				2004 through				through					through				Year Ended December 31,
		June 30,				June 30,				December 31,					March 2,
		2005				2004				2004					2004				2003				2002				2001				2000
		(In millions)
Other Financial Data:
EBITDA(1)		$	77.5			$	55.9			$	143.5				$	33.4			$	100.3			$	113.9			$	113.6			$	89.6
Net cash provided by operating activities			72.7				39.6				135.9					20.3				103.5				60.3				113.5				63.9
Net cash (used) provided by investing activities			(98.7	)			(36.2	)			(133.6	)				(15.3	)			38.3				(53.8	)			(74.0	)			(79.1	)
Net cash (used) provided by financing activities			31.5				(34.9	)			64.9					—				(100.0	)			—				(30.0	)			17.4
Reconciliation of Non-GAAP Measures:
EBITDA(1)		$	77.5			$	55.9			$	143.5				$	33.4			$	100.3			$	113.9			$	113.6			$	89.6
Changes in working capital			(14.9	)			(14.0	)			6.9					(13.2	)			21.8				(20.4	)			7.5				(15.5	)
Non-cash hedge gain(2)			(2.5	)			—				(7.9	)				—				(2.0	)			(23.2	)			—				—
Amortization/other			0.6				0.3				0.8					—				—				(0.1	)			0.6				0.7
Stock compensation expense			9.5				—				—					—				—				—				—				—
Net interest expense			(3.0	)			(2.6	)			(5.8	)				0.1				(6.2	)			(9.9	)			(8.2	)			(10.9	)
Income tax expense			5.5				—				(1.6	)				—				(10.4	)			—				—				—
Net cash provided by operating activities		$	72.7			$	39.6			$	135.9				$	20.3			$	103.5			$	60.3			$	113.5			$	63.9

(1)

EBITDA means earnings before interest, income taxes, depreciation, depletion and amortization. For the six months ended June 30, 2005, EBITDA includes $9.5 million in non-cash stock compensation expense related to restricted stock and stock options granted in the first quarter of 2005. We believe that EBITDA is a widely accepted financial indicator that provides additional information about our ability to meet our future requirements for debt service, capital expenditures and working capital, but EBITDA should not be considered in isolation or as a substitute for net income, operating income, net cash provided by

	operating activities or any other measure of financial performance presented in accordance with generally accepted accounting principles or as a measure of a company’s profitability or liquidity.
(2)	In accordance with SFAS No. 133 “Accounting for Derivative Instruments and Hedging Activities,” as amended by SFAS No. 137 and No. 138, we de-designated our contracts effective December 2, 2001 after the counterparty (an affiliate of Enron Corp.) filed for bankruptcy and recognized all market value changes subsequent to such de-designation in our earnings. The value recorded up to the time of de-designation and included in Accumulated Other Comprehensive Income (“AOCI”), has reversed out of AOCI and into earnings as the original corresponding production, as hedged by the contracts, is produced. We have designated subsequent hedge contracts as cash flow hedges with gains and losses resulting from the transactions recorded at market value in AOCI, as appropriate, until recognized as operating income in our Statement of Operations as the physical production hedged by the contracts is delivered.

												Years Ended
				Six Months Ended June 30,								December 31
				2005				2004				2004				2003				2002
				(In millions, except production data)
Statement of Operations Data:
	Oil and natural gas revenues(1)			$	234.3			$	199.1			$	453.1			$	342.0			$	228.9
	Direct Operating Expenses:
		Lease operating expenses			35.8				42.1				80.1				45.7				52.1
		Transportation			1.9				0.8				2.2				2.7				3.8
		Production taxes			1.2				0.8				1.5				1.5				1.0
	Total direct operating expenses				38.9				43.7				83.8				49.9				56.9
	Revenues in excess of direct operating expenses			$	195.4			$	155.4			$	369.3			$	292.1			$	172.0
Summary Production Data:
	Production Data:
	Natural gas (MMcf)				29,998				28,991				61,684				58,785				50,566
	Oil and condensate (MBbls)				1,320				1,314				2,624				2,143				1974
	Natural gas liquids (MBbls)				478				79				606				2				6
	Total (MMcfe)				40,786				37,349				81,064				71,655				62,446
	Per day (MMcfe)				225				205				221				196				171
	Per Mcfe:
	Average realized sales price(1)			$	5.75				5.33				5.59				4.77				3.67
	Lease operating expenses			$	0.88				1.13				0.99				0.64				0.83
	Transportation			$	0.05				0.02				0.03				0.04				0.06
	Production taxes			$	0.03				0.02				0.02				0.02				0.02
Capital Expenditure Data:
	Exploration			$	32.8			$	19.6			$	28.3			$	39.7			$	17.5
	Development				30.1				45.6				70.0				74.7				70.8
	Acquisition				—				66.8				87.2				168.5				3.3
	Total capital expenditures			$	62.9			$	132.0			$	185.5			$	282.9			$	91.6

(1)	Includes effects of hedging.

			As of and for the
			Six Months Ended				For the Year Ended
			June 30, 2005				December 31, 2004
			(In thousands, except per share
			and proved reserve data)
OPERATING RESULTS:
	Revenues		$	341,915			$	667,326
	Net income		$	56,308			$	104,634
Earnings per share
	Basic		$	0.68			$	1.30
	Diluted		$	0.68			$	1.30
Weighted average shares outstanding
	Basic			82,613				80,385
	Diluted			82,878				80,385
BALANCE SHEET DATA:
	Total assets		$	2,079,457
	Total debt		$	299,000
	Stockholders’ equity		$	1,248,306
ESTIMATED PROVED RESERVES (as of December 31, 2004):
	Oil (MBbls)							25,905
	Gas (MMcf)							421,741
	Equivalent (MMcfe)							577,173
	Proved developed percentage							63.7%

				Mariner
								Combined
				Historical				Pro Forma
Earnings (loss) per share —
	Six months ended June 30, 2005(1)
		Basic		$	0.90			$	0.68
		Diluted		$	0.89			$	0.68
	Year ended December 31, 2004(2)
		Basic		$	2.30			$	1.30
		Diluted		$	2.30			$	1.30
Book Value per share — As of June 30, 2005(3)				$	6.29			$	15.11
Cash dividends declared per common share				$	—			$	—

(1)	Mariner’s historical basic and diluted earnings per share calculation as of June 30, 2005 assumes Mariner had 31,975,754 and 32,241,159 shares of common stock outstanding, respectively. Mariner’s pro forma basic and diluted earnings per share calculation as of June 30, 2005 assumes Mariner had 82,612,764 and 82,878,169 shares of common stock outstanding, respectively.
(2)	Mariner’s historical basic and diluted earnings per share calculation as of December 31, 2004 assumes Mariner had 29,748,130 and 29,748,130 shares of common stock outstanding, respectively. Mariner’s pro forma basic and diluted earnings per share calculation as of December 31, 2004 assumes Mariner had 80,385,140 and 80,385,140 shares of common stock outstanding, respectively.
(3)	Book value per share calculation assumes that Mariner had 31,975,754 shares of common stock outstanding and 82,612,764 combined pro forma shares of common stock outstanding as of June 30, 2005.

RISK FACTORS

      In addition to the other information that we have included and incorporated by reference in this proxy statement/ prospectus-information statement, you should carefully read and consider the following factors in determining whether to vote to adopt the merger agreement and the other proposals at the Mariner special meeting.

Risks Related to the Spin-Off and the Merger

      The market price of our common stock could decline as a result of sales of a large number of shares in the market after the completion of the spin-off and merger or the perception that these sales could occur. These sales, or the possibility that these sales may occur, also might make it more difficult for us to obtain additional capital by selling equity securities in the future at a time and at a price that we deem appropriate.

      Immediately after the merger, Forest shareholders will hold, in the aggregate, approximately 58% of our common stock on a pro forma basis. Currently, Forest shareholders include index funds tied to various stock indices, and institutional investors subject to various investing guidelines. Because we may not be included in these indices at the time of the merger or may not meet the investing guidelines of some of these institutional investors, these index funds and institutional investors may decide to sell the Mariner common stock they receive in the merger. These sales may negatively affect the price of our common stock.

      Historically, Forest has operated with properties in diverse geographic locations, including the Gulf Coast, the Western United States, Alaska, Canada and other international locations. In contrast, following the spin-off and merger, Mariner will operate as a stand-alone oil and gas exploration, development and production company with operations primarily in the Gulf of Mexico and in West Texas. Shareholders of Forest who chose to invest in a geographically diverse company may not wish to continue to invest in one that is less geographically diverse, such as Mariner. As a result, such shareholders may seek to sell the shares of our common stock received in the merger.

      There is a significant degree of difficulty and management involvement inherent in the process of integrating the Forest Gulf of Mexico operations. These difficulties include:

      The process of integrating operations could cause an interruption of, or loss of momentum in, the activities of our business. Members of our senior management may be required to devote considerable amounts of time to this integration process, which will decrease the time they will have to manage our business. If our senior management is not able to effectively manage the integration process, or if any significant business activities are interrupted as a result of the integration process, our business could suffer.

      The success of the merger will depend, in part, on our ability to realize the anticipated growth opportunities from combining the Forest Gulf of Mexico operations with Mariner. Even if we are able to successfully combine the two businesses, it may not be possible to realize the full benefits of the proved reserves, enhanced growth of production volume, cost savings from operating synergies and other benefits that we currently expect to result from the merger, or realize these benefits within the time frame that is currently expected. The benefits of the merger may be offset by operating losses relating to changes in commodity prices, or in oil and gas industry conditions, or by risks and uncertainties relating to the combined company’s exploratory prospects, or an increase in operating or other costs or other difficulties. If we fail to realize the benefits we anticipate from the merger, stockholders may receive lower returns on our stock than they expect.

      We are developing a plan to integrate the Forest Gulf of Mexico operations with our operations after the merger. Following the merger, we anticipate that from time to time we will incur charges to our earnings in connection with the integration. These charges will include expenses incurred in connection with relocating and retaining employees and increased professional and consulting costs. We also expect to incur significant expenses related to being a public company. We will not be able to quantify the exact amount of these charges or the period(s) in which they will be incurred until after the merger is completed. Some factors affecting the cost of the integration include the timing of the closing of the merger, the training of new employees, the amount of severance and other employee-related payments resulting from the merger, and the limited length of time during which transitional services are provided by Forest.

      Following the spin-off and the merger, the holders of Forest common stock will ultimately become entitled to receive approximately 0.8 shares of Mariner common stock for each Forest share they own. This ratio will not be adjusted for changes in the value of our company or the Forest Gulf of Mexico operations. If our value relative to the Forest Gulf of Mexico operations increases (or the value of the Forest Gulf of Mexico operations decreases relative to our value) prior to the completion of the merger, the market value of the Mariner common stock that Forest shareholders receive in the merger may not reflect the then-current relative values of the individual companies.

      Completion of the spin-off and merger is conditioned upon the receipt of required government consents, approvals, orders and authorizations. While we intend to pursue vigorously all required governmental approvals and do not know of any reason why we would not be able to obtain the necessary approvals in a timely manner, the requirement to receive these approvals before the spin-off and merger could delay the completion of the spin-off and merger, possibly for a significant period of time after Mariner stockholders have approved the merger proposal at the special meeting. In addition, these governmental agencies may attempt to condition their approval of the merger on the imposition of conditions that could have a material adverse effect on our operating results or the value of our common stock after the spin-off and merger are completed. Any delay in the completion of the spin-off and merger could diminish anticipated benefits of the spin-off and merger or result in additional transaction costs, loss of revenue or other effects associated with uncertainty about the transaction. Any uncertainty over the ability of the companies to complete the spin-off and merger could make it more difficult for us to retain key employees or to pursue business strategies. In addition, until the spin-off and merger are completed, the attention of our management may be diverted from ongoing

business concerns and regular business responsibilities to the extent management is focused on matters relating to the transaction, such as obtaining regulatory approvals.

      The spin-off is conditioned on the receipt of a legal opinion to the effect that the spin-off will be treated as a tax-free transaction to Forest and its shareholders for U.S. federal income tax purposes by reason of its qualification under Sections 355 and 368 of the Internal Revenue Code of 1986, as amended. Certain actions taken (and certain omissions) by Forest or Mariner after the spin-off could render the spin-off taxable on a retroactive basis.

      The tax sharing agreement imposes ongoing restrictions on Forest and on us to ensure that applicable statutory requirements under the Internal Revenue Code and applicable Treasury regulations continue to be met so that the spin-off remains tax-free to Forest and its shareholders. As a result of these restrictions, our ability to engage in certain transactions, such as the redemption of our common stock, the issuance of equity securities and the utilization of our stock as currency in an acquisition, will be limited for a period of two years following the spin-off.

      In particular, if a change of control of Mariner or Forest Energy Resources occurs as a result of a plan or series of related transactions that includes the spin-off, the distribution of the shares of Forest Energy Resources common stock may become taxable to Forest. Under Section 355(e) of the Internal Revenue Code, any issuance or acquisition of our stock or Forest Energy Resources’ stock within two years following the spin-off would be presumed to be part of such a plan unless Forest or we were able to rebut the presumption that the issuance or acquisition was part of the spin-off plan. A change of control that results in tax under Section 355(e) of the Internal Revenue Code may occur if, within the four-year period ending two years after the spin-off, a 50% or greater interest in Mariner or Forest Energy Resources is acquired. As a result of the merger, an approximate 42% interest in Mariner and Forest Energy Resources will be treated as already having been acquired. Under U.S. Treasury regulations, certain safe harbors exist under which certain issuances of shares of Mariner and Forest Energy Resources will not be deemed part of the same plan as the spin-off. Among other safe harbors, safe harbors exist for transactions if specific timing conditions are met as to when agreements or substantial negotiations relating to such transactions occur and a safe harbor exists for certain issuances pursuant to compensatory employment-related arrangements.

      If Forest or Mariner takes or permits an action to be taken (or omits to take an action) that causes the spin-off to become taxable, the relevant entity generally will be required to bear the cost of the resulting tax liability to the extent that the liability results from the actions or omissions of that entity. If the spin-off became taxable, Forest would be expected to recognize a substantial amount of income, which would result in a material amount of taxes. Any such taxes allocated to us would be expected to be material to us, and could cause our business, financial condition and operating results to suffer.

      These restrictions may reduce our ability to engage in certain business transactions that otherwise might be advantageous to us and our stockholders and could have a negative impact on our business and stockholder value.

      When considering the recommendations of our board of directors, you should be aware that some of our directors and executive officers have interests and arrangements that may be different from your interests as stockholders, including:

See “Interests of Certain Persons in the Merger” beginning on page 29.

Risks Related to the Combined Operations After the Merger

      Our revenues, profitability and cash flow depend substantially upon the prices and demand for oil and natural gas. The markets for these commodities are volatile and even relatively modest drops in prices can affect significantly our financial results and impede our growth. Oil and natural gas prices are currently at or near historical highs and may fluctuate and decline significantly in the near future. Prices for oil and natural gas fluctuate in response to relatively minor changes in the supply and demand for oil and natural gas, market uncertainty and a variety of additional factors beyond our control, such as:

      Further, oil prices and natural gas prices do not necessarily fluctuate in direct relationship to each other. Because approximately 73% of our pro forma estimated proved reserves as of December 31, 2004 (including reserves of the Forest Gulf of Mexico operations) were natural gas reserves, our financial results are more sensitive to movements in natural gas prices. Lower oil and natural gas prices may not only decrease our revenues on a per unit basis but also may reduce the amount of oil and natural gas that we can produce economically. This may result in our having to make substantial downward adjustments to our estimated proved reserves and could have a material adverse effect on our financial condition and results of operations.

      Estimating oil and natural gas reserves is complex and inherently imprecise. It requires interpretation of the available technical data and making many assumptions about future conditions, including price and other economic conditions. In preparing estimates we and Forest project production rates and timing of development expenditures. We and Forest also analyze the available geological, geophysical, production and engineering data. The extent, quality and reliability of this data can vary. This process also requires economic assumptions about matters such as oil and natural gas prices, drilling and operating expenses, capital expenditures, taxes and availability of funds. If the interpretations or assumptions we use in arriving at our estimates prove to be inaccurate, the amount of oil and natural gas that we ultimately recover may differ materially from the

estimated quantities and net present value of reserves shown in this proxy statement/prospectus-information statement. See “Mariner — Estimated Proved Reserves” for information about our oil and gas reserves and “The Forest Gulf of Mexico Operations — Estimated Proved Reserves” for more information about the oil and gas reserves of the Forest Gulf of Mexico operations.

      Actual future production, oil and natural gas prices, revenues, taxes, development expenditures, operating expenses and quantities of recoverable oil and natural gas reserves most likely will vary from our and Forest’s estimates, perhaps significantly. In addition, we may adjust estimates of proved reserves to reflect production history, results of exploration and development, prevailing oil and natural gas prices and other factors, many of which are beyond our control. At December 31, 2004, 37% of our pro forma proved reserves (including reserves of the Forest Gulf of Mexico operations) were proved undeveloped.

      The present value of future net revenues from our proved reserves and the proved reserves of the Forest Gulf of Mexico operations referred to in this proxy statement/prospectus-information statement is not necessarily the actual current market value of our estimated oil and natural gas reserves. In accordance with SEC requirements, we and Forest base the estimated discounted future net cash flows from our proved reserves and the proved reserves of the Forest Gulf of Mexico operations on fixed prices and costs as of the date of the estimate. Actual future prices and costs fluctuate over time and may differ materially from those used in the present value estimate. In addition, discounted future net cash flows are estimated assuming that royalties to the MMS with respect to our affected offshore Gulf of Mexico properties will be paid or suspended for the life of the properties based upon oil and natural gas prices as of the date of the estimate. See “Mariner — Royalty Relief.” Since actual future prices fluctuate over time, royalties may be required to be paid for various portions of the life of the properties and suspended for other portions of the life of the properties.

      The timing of both the production and expenses from the development and production of oil and natural gas properties will affect both the timing of actual future net cash flows from our proved reserves and the proved reserves of the Forest Gulf of Mexico operations and their present value. In addition, the 10% discount factor that we and Forest use to calculate the net present value of future net cash flows for reporting purposes in accordance with the SEC’s rules may not necessarily be the most appropriate discount factor. The effective interest rate at various times and the risks associated with our business or the oil and gas industry in general will affect the appropriateness of the 10% discount factor in arriving at an accurate net present value of future net cash flows.

      Our future oil and natural gas production depends on our success in finding or acquiring additional reserves. If we fail to replace reserves through drilling or acquisitions, our level of production and cash flows will be affected adversely. In general, production from oil and natural gas properties declines as reserves are depleted, with the rate of decline depending on reservoir characteristics. Our total proved reserves decline as reserves are produced unless we conduct other successful exploration and development activities or acquire properties containing proved reserves, or both. Our ability to make the necessary capital investment to maintain or expand our asset base of oil and natural gas reserves would be impaired to the extent cash flow from operations is reduced and external sources of capital become limited or unavailable. We may not be successful in exploring for, developing or acquiring additional reserves.

      Due to high production rates, production of reserves from reservoirs in the Gulf of Mexico generally declines more rapidly than from reservoirs in other producing regions. As a result, our reserve replacement needs from new prospects may be greater than those of other oil and gas companies. If the merger is consummated, the proportion of short-lived Gulf of Mexico properties relative to our total properties will increase substantially. Also, our revenues and return on capital will depend significantly on prices prevailing

during these relatively short production periods. Our ability to slow or shut in production from producing wells during periods of low prices for oil and natural gas may be limited by reservoir characteristics or by our need to generate revenues to fund ongoing capital commitments or repay debt.

      A substantial portion of our exploration and production activities are located in the Gulf of Mexico. This concentration of activity makes us more vulnerable than some other industry participants to the risks associated with the Gulf of Mexico, including delays and increased costs relating to adverse weather conditions such as hurricanes, which are common in the Gulf of Mexico during certain times of the year, drilling rig and other oilfield services and compliance with environmental and other laws and regulations.

      Exploration activities involve numerous risks, including the risk that no commercially productive oil or natural gas reservoirs will be discovered. In addition, the future cost and timing of drilling, completing and producing wells is often uncertain. Furthermore, drilling operations may be curtailed, delayed or canceled as a result of a variety of factors, including:

      Our decisions to purchase, explore, develop and exploit prospects or properties depend in part on data obtained through geophysical and geological analyses, production data and engineering studies, the results of which are often uncertain. Even when used and properly interpreted, 3-D seismic data and visualization techniques only assist geoscientists and geologists in identifying subsurface structures and hydrocarbon indicators. They do not allow the interpreter to know conclusively if hydrocarbons are present or producible economically. In addition, the use of 3-D seismic and other advanced technologies require greater predrilling expenditures than traditional drilling strategies. Because of these factors, we could incur losses as a result of exploratory drilling expenditures. Poor results from exploration activities could have a material adverse effect on our future cash flows, ability to replace reserves and results of operations.

      Our business is subject to all of the operating risks associated with drilling for and producing oil and natural gas, including:

      If any of these events occur, we could incur substantial losses as a result of injury or loss of life, severe damage to and destruction of property, natural resources and equipment, pollution and other environmental damage, clean-up responsibilities, regulatory investigation and penalties, suspension of our operations and repairs to resume operations.

      Offshore operations are also subject to a variety of operating risks specific to the marine environment, such as capsizing, collisions and damage or loss from hurricanes or other adverse weather conditions. These conditions can cause substantial damage to facilities and interrupt production. As a result, we could incur substantial liabilities that could reduce or eliminate the funds available for exploration, development or leasehold acquisitions, or result in loss of equipment and properties.

      In September 2004, August 2005 and September 2005 we incurred damage from Hurricanes Ivan, Katrina and Rita, respectively. The hurricanes damaged some of our owned platforms and facilities and the host facilities at some of our projects, and as a result we experienced temporary shut-in production and project startup delays. Hurricanes Katrina and Rita also damaged some of the assets included in the Forest Gulf of Mexico operations. For more information on the impact of recent hurricanes on Mariner’s operations and the Forest Gulf of Mexico operations, see “Management’s Discussion and Analysis of Financial Condition and Results of Operations of Mariner — Recent Developments” beginning on page 86 and “Management’s Discussion and Analysis of Financial Condition and Results of Operations of the Forest Gulf of Mexico Operations — Recent Developments” beginning on page 124.

      Exploration for oil or natural gas in the deepwater of the Gulf of Mexico generally involves greater operational and financial risks than exploration on the shelf. As of December 31, 2004, on a pro forma basis (including the Forest Gulf of Mexico operations), approximately 18% of our estimated proved reserves, representing approximately 20% of our PV10, are located in the deepwater of the Gulf of Mexico. Deepwater drilling generally requires more time and more advanced drilling technologies, involving a higher risk of technological failure and usually higher drilling costs. Our deepwater wells use subsea completion techniques with subsea trees tied back to host production facilities with flow lines. The installation of these subsea trees and flow lines requires substantial time and the use of advanced remote installation mechanics. These operations may encounter mechanical difficulties and equipment failures that could result in significant cost overruns. Furthermore, the deepwater operations generally lack the physical and oilfield service infrastructure present in the shallow waters of the Gulf of Mexico. As a result, a significant amount of time may elapse between a deepwater discovery and our marketing of the associated oil or natural gas, increasing both the financial and operational risk involved with these operations. Because of the lack and high cost of infrastructure, some reserve discoveries in the deepwater may never be produced economically.

      We enter into hedging arrangements from time to time to reduce our exposure to fluctuations in oil and natural gas prices and to achieve more predictable cash flow. These financial arrangements typically take the form of price swap contracts and costless collars. Hedging arrangements expose us to the risk of financial loss in some circumstances, including situations when the other party to the hedging contract defaults on its contract or production is less than expected. During periods of high commodity prices, hedging arrangements

may limit significantly the extent to which we can realize financial gains from such higher prices. For example, in calendar year 2004, on a pro forma basis (including the Forest Gulf of Mexico operations), our hedging arrangements reduced the benefit we received from increases in the prices for oil and natural gas by approximately $76.9 million. Although we currently maintain an active hedging program, we may choose not to engage in hedging transactions in the future. As a result, we may be affected adversely during periods of declining oil and natural gas prices.

      We depend on our ability to obtain financing beyond our cash flow from operations. Historically, we have financed our business plan and operations primarily with internally generated cash flow, bank borrowings, proceeds from the sale of oil and natural gas properties, entering into exploration arrangements with other parties, the issuance of public debt, privately raised equity and, prior to the bankruptcy of Enron Corp. (our indirect parent company until March 2, 2004), borrowings from Enron affiliates. In the future, we will require substantial capital to fund our business plan and operations. We expect to be required to meet our needs from our excess cash flow, debt financings and additional equity offerings (subject to certain federal tax limitations during the two-year period following the spin-off). Sufficient capital may not be available on acceptable terms or at all. If we cannot obtain additional capital resources, we may curtail our drilling, development and other activities or be forced to sell some of our assets on unfavorable terms.

      The issuance of additional debt would require that a portion of our cash flow from operations be used for the payment of interest on our debt, thereby reducing our ability to use our cash flow to fund working capital, capital expenditures, acquisitions and general corporate requirements, which could place us at a competitive disadvantage relative to other competitors. Additionally, if revenues decrease as a result of lower oil or natural gas prices, operating difficulties or declines in reserves, our ability to obtain the capital necessary to undertake or complete future exploration and development programs and to pursue other opportunities may be limited, which could result in a curtailment of our operations relating to exploration and development of our prospects, which in turn could result in a decline in our oil and natural gas reserves.

      Properties we acquire, including the Forest Gulf of Mexico properties, may not produce as expected, may be in an unexpected condition and may subject us to increased costs and liabilities, including environmental liabilities. The reviews we conduct of acquired properties prior to acquisition are not capable of identifying all potential adverse conditions. Generally, it is not feasible to review in depth every individual property involved in each acquisition. Ordinarily, we will focus our review efforts on the higher value properties or properties with known adverse conditions and will sample the remainder. However, even a detailed review of records and properties may not necessarily reveal existing or potential problems or permit a buyer to become sufficiently familiar with the properties to assess fully their condition, any deficiencies, and development potential. Inspections may not always be performed on every well, and environmental problems, such as ground water contamination, are not necessarily observable even when an inspection is undertaken.

      Market conditions, the unavailability of satisfactory oil and natural gas transportation or the remote location of our drilling operations may hinder our access to oil and natural gas markets or delay our production. The availability of a ready market for our oil and natural gas production depends on a number of factors, including the demand for and supply of oil and natural gas and the proximity of reserves to pipelines or trucking and terminal facilities. In deepwater operations, the availability of a ready market depends on the proximity of and our ability to tie into existing production platforms owned or operated by others and the

ability to negotiate commercially satisfactory arrangements with the owners or operators. We may be required to shut in wells or delay initial production for lack of a market or because of inadequacy or unavailability of pipeline or gathering system capacity. When that occurs, we are unable to realize revenue from those wells until the production can be tied to a gathering system. This can result in considerable delays from the initial discovery of a reservoir to the actual production of the oil and natural gas and realization of revenues.

      Shortages or the high cost of drilling rigs, equipment, supplies or personnel could delay or affect adversely our exploration and development operations, which could have a material adverse effect on our financial condition and results of operations. An increase in drilling activity in the U.S. or the Gulf of Mexico could increase the cost and decrease the availability of necessary drilling rigs, equipment, supplies and personnel.

      We operate in a highly competitive environment for acquiring prospects and productive properties, marketing oil and natural gas and securing equipment and trained personnel. Many of our competitors are major and large independent oil and natural gas companies, and possess and employ financial, technical and personnel resources substantially greater than ours. Those companies may be able to develop and acquire more prospects and productive properties than our financial or personnel resources permit. Our ability to acquire additional prospects and discover reserves in the future will depend on our ability to evaluate and select suitable properties and consummate transactions in a highly competitive environment. Also, there is substantial competition for capital available for investment in the oil and natural gas industry. Larger competitors may be better able to withstand sustained periods of unsuccessful drilling and absorb the burden of changes in laws and regulations more easily than we can, which would adversely affect our competitive position. We may not be able to compete successfully in the future in acquiring prospective reserves, developing reserves, marketing hydrocarbons, attracting and retaining quality personnel and raising additional capital.

      From time to time, we enter into farm-out agreements to fund a portion of the exploration and development costs of our prospects. Moreover, other companies operate some of the other properties in which we have an ownership interest. Liquidity and cash flow problems encountered by our partners and co-owners of our properties may lead to a delay in the pace of drilling or project development that may be detrimental to a project.

      In addition, our farm-out partners and working interest owners may be unwilling or unable to pay their share of the costs of projects as they become due. In the case of a farm-out partner, we may have to obtain alternative funding in order to complete the exploration and development of the prospects subject to the farm-out agreement. In the case of a working interest owner, we may be required to pay the working interest owner’s share of the project costs. We cannot assure you that we would be able to obtain the capital necessary in order to fund either of these contingencies.

      Other companies operate some of the properties in which we have an interest. As a result, we have a limited ability to exercise influence over operations for these properties or their associated costs. Our dependence on the operator and other working interest owners for these projects and our limited ability to influence operations and associated costs could materially adversely affect the realization of our targeted returns on capital in drilling or acquisition activities. The success and timing of drilling and development activities on properties operated by others therefore depend upon a number of factors that are outside of our control, including timing and amount of capital expenditures, the operator’s expertise and financial resources, approval of other participants in drilling wells and selection of technology.

      Exploration for and development, production and sale of oil and natural gas in the U.S. and the Gulf of Mexico are subject to extensive federal, state and local laws and regulations, including environmental and health and safety laws and regulations. We may be required to make large expenditures to comply with these environmental and other requirements. Matters subject to regulation include, among others, environmental assessment prior to development, discharge and emission permits for drilling and production operations, drilling bonds, and reports concerning operations and taxation.

      Under these laws and regulations, and also common law causes of action, we could be liable for personal injuries, property damage, oil spills, discharge of pollutants and hazardous materials, remediation and clean-up costs and other environmental damages. Failure to comply with these laws and regulations or to obtain or comply with required permits may result in the suspension or termination of our operations and subject us to remedial obligations as well as administrative, civil and criminal penalties. Moreover, these laws and regulations could change in ways that substantially increase our costs. We cannot predict how agencies or courts will interpret existing laws and regulations, whether additional or more stringent laws and regulations will be adopted or the effect these interpretations and adoptions may have on our business or financial condition. For example, the Oil Pollution Act of 1990 (the “OPA”) imposes a variety of regulations on “responsible parties” related to the prevention of oil spills. The implementation of new, or the modification of existing, environmental laws or regulations promulgated pursuant to the OPA could have a material adverse impact on us. Further, Congress or the MMS could decide to limit exploratory drilling or natural gas production in additional areas of the Gulf of Mexico. Accordingly, any of these liabilities, penalties, suspensions, terminations or regulatory changes could have a material adverse effect on our financial condition and results of operations. See “Mariner — Regulation” for more information on our regulatory and environmental matters.

      We maintain insurance for some, but not all, of the potential risks and liabilities associated with our business. For some risks, we may not obtain insurance if we believe the cost of available insurance is excessive relative to the risks presented. As a result of market conditions, premiums and deductibles for certain insurance policies can increase substantially, and in some instances, certain insurance may become unavailable or available only for reduced amounts of coverage. As a result, we may not be able to renew our existing insurance policies or procure other desirable insurance on commercially reasonable terms, if at all. Although we maintain insurance at levels we believe are appropriate and consistent with industry practice, we are not fully insured against all risks, including drilling and completion risks that are generally not recoverable from third parties or insurance. In addition, pollution and environmental risks generally are not fully insurable. Losses and liabilities from uninsured and underinsured events and delay in the payment of insurance proceeds could have a material adverse effect on our financial condition and results of operations. The impact of Hurricanes Katrina and Rita have resulted in escalating insurance costs and less favorable coverage terms.

      Our exploratory drilling success will depend, in part, on our ability to attract and retain experienced explorationists and other professional personnel. Competition for explorationists and engineers with experience in the Gulf of Mexico is intense. If we cannot retain our current personnel or attract additional experienced personnel, or if employees of the Forest Gulf of Mexico operations terminate their employment prior to the completion of the merger, our ability to compete in the Gulf of Mexico could be adversely affected. In addition, the use of 3-D seismic and other advanced technologies requires experienced technical personnel whom we may be unable to retain or attract.

      We believe that our operations are dependent to a significant extent on the efforts of key employees, most of whom have more than 20 years of experience in the oil and gas business. The loss of the services of any of these key individuals could have a material adverse effect on us. We do not maintain any insurance against the loss of any of these individuals.

      Our bank credit agreement includes a change of control provision that provides in part that an event of default will occur if Scott Josey ceases to be the Chief Executive Officer or President of Mariner or to be actively engaged in the executive management of Mariner and is not replaced with an individual of comparable qualifications within six months. Therefore, if Mr. Josey were to leave our employment and we were unable to obtain the services of another senior executive with comparable experience to replace him, our banks would have the right to declare our bank loans due and we would have to seek alternative financing.

Risks Related to our Common Stock After the Merger

      We are a private company, and there is no public market for our common stock. An active market for our common stock may not develop or may not be sustained after this offering. In addition, we cannot assure you as to the liquidity of any such market that may develop or the price that our stockholders may obtain for their shares of our common stock.

      Even if an active trading market develops, the market price for shares of our common stock may be highly volatile and could be subject to wide fluctuations. Some of the factors that could negatively affect our share price include:

      We do not expect to declare or pay any cash or other dividends in the foreseeable future on our common stock. Our existing revolving credit facility restricts our ability to pay cash dividends on our common stock, and we may also enter into other credit agreements or other borrowing arrangements in the future that restrict our ability to declare or pay cash dividends on our common stock.

      If the merger is completed, the current owners of Mariner’s common stock will experience substantial and immediate dilution from the issuance of shares of Mariner common stock to Forest shareholders, such that the Mariner stockholders will own approximately 42% of the Mariner common stock following the merger. We may in the future issue our previously authorized and unissued securities, resulting in the dilution of the ownership interests of our present stockholders. We are currently authorized to issue 70 million shares of common stock and 20 million shares of preferred stock with such designations, preferences and rights as determined by our board of directors. As a result of the proposed amendment to our certificate of incorporation, our authorized shares would be increased to 180 million shares of common stock and 20 million shares of preferred stock. As of the date of this proxy statement/ prospectus-information statement, 35,615,400 shares of common stock were outstanding. This includes 2,267,270 shares of common stock that have been granted to certain employees as restricted stock pursuant to our equity participation plan. In addition, we have reserved an additional 2,000,000 shares for future issuance to employees and directors as restricted stock or stock option awards pursuant to our stock incentive plan, of which options to purchase 809,000 shares have already been granted. Pursuant to the proposed addition of shares to our stock incentive plan, the maximum number of shares would, if the proposal is approved, be increased to 6.5 million shares. The potential issuance of such additional shares of common stock may create downward pressure on the trading price of our common stock. We may also issue additional shares of our common stock or other securities that are convertible into or exercisable for common stock (subject to certain federal tax limitations during the two-year period following the spin-off) in connection with the hiring of personnel, future acquisitions, future public offerings or private placements of our securities for capital raising purposes, or for other business purposes. Future sales of substantial amounts of our common stock, or the perception that sales could occur, could have a material adverse effect on the price of our common stock.

      The existence of some provisions in our organizational documents and under Delaware law could delay or prevent a change in control of our company, which could adversely affect the price of our common stock. The provisions in our certificate of incorporation and bylaws that could delay or prevent an unsolicited change in control of our company include a staggered board of directors, board authority to issue preferred stock, and advance notice provisions for director nominations or business to be considered at a stockholder meeting. In addition, Delaware law imposes restrictions on mergers and other business combinations between us and any holder of 15% or more of our outstanding common stock. See “Description of Mariner Capital Stock.”

CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING STATEMENTS

      Various statements in this proxy statement/ prospectus-information statement, including those that express a belief, expectation, or intention, as well as those that are not statements of historical fact, are forward-looking statements. The forward-looking statements may include projections and estimates concerning the timing and success of specific projects and our future production, revenues, income and capital spending. Our forward-looking statements are generally accompanied by words such as “estimate,” “project,” “predict,” “believe,” “expect,” “anticipate,” “potential,” “plan,” “goal” or other words that convey the uncertainty of future events or outcomes. The forward-looking statements in this proxy statement/ prospectus-information statement speak only as of the date of this proxy statement/ prospectus-information statement; we disclaim any obligation to update these statements unless required by securities law, and we caution you not to rely on them unduly. We have based these forward-looking statements on our current expectations and assumptions about future events. While our management considers these expectations and assumptions to be reasonable, they are inherently subject to significant business, economic, competitive, regulatory and other risks, contingencies and uncertainties, most of which are difficult to predict and many of which are beyond our control. We disclose important factors that could cause our actual results to differ materially from our expectations under “Risk Factors,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations of the Forest Gulf of Mexico Operations,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations of Mariner” and elsewhere in this proxy statement/ prospectus-information statement. These risks, contingencies and uncertainties relate to, among other matters, the following:

THE MARINER SPECIAL MEETING

Purpose, Time and Place

      The Mariner special meeting will be held on                     ,                     , 2005 at 10:00 a.m., Central Standard Time, at                                                                  , Houston, Texas             . The purpose of the Mariner special meeting is:

We currently expect that no other matters will be considered at the special meeting.

Recommendation of the Mariner Board of Directors

      The Mariner board of directors has determined that the merger is fair to and in the best interests of Mariner and its stockholders, and that the merger agreement is advisable. The Mariner board of directors has unanimously approved the merger agreement, the proposed amendment to the certificate of incorporation and the proposed amendment and restatement of the stock incentive plan, and recommends that the Mariner stockholders vote “for” the adoption of the merger agreement and the other proposals.

Record Date; Stock Entitled to Vote; Quorum

      Stockholders of record of Mariner common stock at the close of business on                     , 2005, the record date for the Mariner special meeting, are entitled to receive notice of, and have the right to vote at, the Mariner special meeting and any reconvened meeting following any adjournment or postponement of the meeting. On the record date, approximately                    shares of Mariner common stock were issued and outstanding. Stockholders of record of shares of Mariner common stock on the record date are each entitled to one vote per share on the proposals.

      A quorum of stockholders is necessary to have a valid meeting of stockholders. The holders of a majority of the stock issued and outstanding and entitled to vote at the meeting, present in person or represented by proxy, will constitute a quorum at the Mariner special meeting.

      Abstentions and broker “non-votes” count as present for establishing a quorum. A broker “non-vote” occurs on an item when a broker is not permitted to vote on that item without instructions from the beneficial owner of the shares and no instructions are given. We expect that, in the event that a quorum is not present at the Mariner special meeting, the meeting will be adjourned or postponed to solicit additional proxies.

Votes Required

      Adoption of the merger agreement and approval of the other proposals will require the affirmative vote of the holders of a majority of the shares of Mariner common stock outstanding on the record date. For purposes of the vote, abstentions will be counted and have the same effect as a vote “against” the proposals. In addition, failing to vote or to instruct your broker to vote will have the same effect as a vote “against” the proposals.

Voting by Proxy

      Stockholders of record may vote their stock by:

If a proxy card is signed by a stockholder of record and returned without specific voting instructions, the stock represented by the proxy will be voted “for” the proposals presented at the Mariner special meeting.

      Stockholders whose shares of Mariner common stock are held in the name of a bank, broker or other fiduciary must either direct the record holder of their shares of Mariner common stock as to how to vote their shares of Mariner common stock or obtain a proxy from the record holder to vote at the Mariner special meeting.

      Stockholders of record may revoke their proxies at any time prior to the time their proxies are voted at the Mariner special meeting. Stockholders can revoke their proxies and change their votes by:

      If your shares of Mariner common stock are held in the name of a bank, broker or other fiduciary and you have directed such person(s) to vote your shares of Mariner common stock, you should instruct such person(s) to change your vote or obtain a legal proxy to do so yourself.

      Any written notice of a revocation of a proxy should be sent to the following address: