Filed Pursuant to Rule 424(b)(3)
Registration No. 333-137088

Prospectus Supplement No. 4

(To Prospectus dated September 19, 2006)

$287,500,000

2.25% Convertible Senior Notes due 2036
and up to 4,837,677 Shares of
Common Stock Issuable Upon Conversion of the Notes

This document supplements the prospectus dated September 19, 2006, relating to the offering for resale of our 2.25% Convertible Senior Notes due 2036, and the shares of our common stock issuable upon conversion of the notes. The information in this prospectus supplement replaces and supersedes the information set forth under the heading “Selling security holders” and the “Plan of distribution” in the prospectus dated September 19, 2006.

Our common stock is listed on the New York Stock Exchange under the symbol “GPI.” On January 16, 2007, the closing sale price of our common stock on the New York Stock Exchange was $54.51 per share.

See “Risk factors” beginning on page 5 of the prospectus for a discussion of certain risks that you should consider in connection with an investment in the notes.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is January 17, 2007.

Selling security holders

On June 26, 2006, we issued and sold a total of $287,500,000 aggregate principal amount of the notes in a private placement to certain initial purchasers. The initial purchasers have advised us that they resold the notes in transactions exempt from the registration requirements of the Securities Act of 1933, as amended, to “qualified institutional buyers” (as defined in Rule 144A under the Securities Act) in compliance with Rule 144A. The selling security holders, which term includes their transferees, pledgees, donees and successors, may from time to time offer and sell pursuant to this prospectus any and all of the notes and the shares of our common stock issuable upon conversion of the notes.

The notes and our shares of common stock to be issued upon conversion of the notes are being registered pursuant to a registration rights agreement between us and the initial purchasers. In that agreement, we undertook to file a registration statement with regard to the notes and our shares of common stock issuable upon conversion of the notes and, subject to certain exceptions, to keep that registration statement effective until the date there are no longer any registrable securities. See “Description of notes—Registration rights.” The registration statement to which this prospectus relates is intended to satisfy our obligations under that agreement.

The selling security holders named below have advised us that they currently intend to sell the notes and our shares of common stock set forth below pursuant to this prospectus. Additional selling security holders may choose to sell notes and our shares of common stock from time to time upon notice to us. None of the selling security holders named below has, within the past three years, held any position, office or other material relationship with us or any of our predecessors or affiliates.

Unless the securities were purchased pursuant to this registration statement, before a security holder not named below may use this prospectus in connection with an offering of securities, this prospectus will be amended or supplemented to include the name and amount of notes and common stock beneficially owned by the selling security holder and the amount of notes and common stock to be offered. Any amended or supplemented prospectus will also disclose whether any selling security holder selling in connection with that amended or supplemented prospectus has held any position, office or other material relationship with us or any of our predecessors or affiliates during the three years prior to the date of the amended prospectus.

The following table is based solely on information provided by the selling security holders. This information represents the most current information provided to us by selling security holders.

																		Number of				Number of
																		Shares of				Shares of
						Percentage								Number of Shares				Common				Common
		Amount of Notes				of Notes				Amount of				of Common Stock				Stock That				Stock Upon
		Beneficially				Beneficially				Notes to Be				Beneficially				May Be				Completion of
		Owned ($)				Owned				Sold ($)(1)				Owned(2)(3)				Sold(1)(3)				Offering(1)
1976 Distribution Trust FBO A.R. Lauder(35)		$	5,000				*			$	5,000				85				85				0
2000 Revocable Trust FBO A.R. Lauder(35)			5,000				*				5,000				84				84				0
Advent Convertible Master Fund LP(35)			6,673,000				2.32				6,673,000				112,285				112,285				0
Alcon Laboratories(35)			720,000				*				720,000				12,115				12,115				0
Alpine Associates(5)(33)			3,060,000				1.06				3,060,000				51,490				51,490				0
Alpine Partners, L.P.(5)(33)			383,000				*				383,000				6,445				6,445				0
Aristeia International Limited(15)			35,200,000				12.24				35,200,000				592,300				592,300				0
Aristeia Partners LP(16)			4,800,000				1.67				4,800,000				80,768				80,768				0
Arlington County Employees Retirement System(35)			1,032,000				*				1,032,000				17,365				17,365				0
Basso Fund Ltd.(28)			35,000				*				35,000				589				589				0
Basso Holdings Ltd.(28)			4,981,000				1.73				4,981,000				83,814				83,814				0
Basso Multi-Strategy Holding Fund Ltd.(28)			589,000				*				589,000				9,911				9,911				0
BP Amoco PLC Master Trust(44)			1,164,000				*				1,164,000				19,586				19,586				0
Brevan Howard Equity Strategies Master Fund Limited(45)			10,000,000				3.48				10,000,000				168,267				168,267				0
British Virgin Islands Social Security Board(35)			238,000				*				238,000				4,005				4,005				0
CALAMOS Market Neutral Income Fund — CALAMOS Investment Trust(7)			6,000,000				2.09				6,000,000				100,960				100,960				0
Canadian Imperial Holdings Inc.(4)(20)			5,000,000				1.74				5,000,000				84,134				84,134				0
CBARB, a segregated account of Geode Capital Master Fund Ltd. (24)			11,500,000				4.00				11,500,000				193,507				193,507				0
Citadel Equity Fund Ltd.(4)(8)			29,500,000				10.26				29,500,000				496,388				496,388				0
City University of New York(35)			206,000				*				206,000				3,467				3,467				0
CNH CA Master Account, L.P.(9)			19,000,000				6.61				19,000,000				319,707				319,707				0
CQS Convertible and Quantitative Strategies Master Fund Limited(10)			3,000,000				1.04				3,000,000				50,480				50,480				0
DBAG London(4)(34)			34,634,000				12.05				34,634,000				582,776				582,776				0
D.E. Shaw Valence Portfolios, L.L.C.(4)(21)			12,000,000				4.17				12,000,000				201,921				201,921				0
Ellington Overseas Partners, Ltd.(17)			3,000,000				1.04				3,000,000				50,480				50,480				0
Five Sticks, L.P.(28)			395,000				*				395,000				6,647				6,647				0
Fore Convertible Master Fund, Ltd.(5)(29)			1,823,000				*				1,823,000				53,190				53,190				0
Fore Erisa Fund, Ltd.(5)(30)			177,000				*				177,000				5,165				5,165				0
Good Steward Trading Co, SPC Class F(32)			57,000				*				57,000				960				960				0
Grace Convertible Arbitrage Fund, Ltd.(22)			4,500,000				1.57				4,500,000				75,720				75,720				0
Grady Hospital(35)			197,000				*				197,000				3,315				3,315				0
HFR Convertible Arbitrage(35)			555,000				*				555,000				9,339				9,339				0
Highbridge International LLC(40)			19,500,000				6.78				19,500,000				328,121				328,121				0
Hotel Union & Hotel Industry of Hawaii Pension Plan Master Trust(44)			175,000				*				175,000				2,945				2,945				0
HSBC Multi Strategy Arbitrage Fund(4)(41)			1,000,000				*				1,000,000				16,827				16,827				0
Independence Blue Cross(35)			597,000				*				597,000				10,046				10,046				0
Inflective Convertible Opportunity Fund I, Limited (4)(18)			2,900,000				1.00				2,900,000				48,797				48,797				0
Inflective Convertible Opportunity Fund I, L.P. (4)(18)			1,500,000				*				1,500,000				25,240				25,240				0
Institutional Benchmark Series-Ivan Segregated Acct. (4)(18)			1,000,000				*				1,000,000				16,827				16,827				0
JPMorgan Securities Inc.(5)(31)			10,720,000				3.73				10,720,000				180,383				180,383				0
KBC Financial Products USA, Inc.(5)(11)			5,000,000				1.74				5,000,000				84,134				84,134				0
Linden Capital LP (25)			22,000,000				7.65				22,000,000				370,187				370,187				0
Lyxor Convertible Arbitrage Fund(35)			272,000				*				272,000				4,577				4,577				0
Lyxor/Inflective Convertible Opportunity Fund (4)(18)			2,000,000				*				2,000,000				33,653				33,653				0
New Orleans Firefighters(35)			120,000				*				120,000				2,020				2,020				0
Occidental Petroleum(35)			458,000				*				458,000				7,707				7,707				0
Police & Firemen of the City of Detroit(35)			437,000				*				437,000				7,354				7,354				0
Polygon Global Opportunities Master Fund (19)			4,000,000				1.39				4,000,000				67,307				67,307				0
Promutual(35)			1,302,000				*				1,302,000				21,909				21,909				0
Rampart Convertible Arbitrage Investors, LLC(39)			2,000,000				*				2,000,000				33,653				33,653				0
San Francisco Public Employees Retirement System(35)			2,040,000				*				2,040,000				34,326				34,326				0
Sunrise Partners Limited Partnership (4)(26)			3,500,000				1.22				3,500,000				58,894				58,894				0
Sutton Brook Capital Portfolio LP(12)			7,000,000				2.43				7,000,000				117,787				117.787				0
The City of Southfield Fire & Police Retirement System(44)			43,000				*				43,000				724				724				0
The Estate of James Campbell CH(44)			122,000				*				122,000				2,053				2,053				0
The Estate of James Campbell EST2(44)			1,000,000				*				1,000,000				16,827				16,827				0
The Grable Foundation(35)			81,000				*				81,000				1,363				1,363				0
Topaz Fund(4)(46)			3,000,000				1.04				3,000,000				50,480				50,480				0
Trustmark(35)			282,000				*				282,000				4,746				4,746				0
UBS O’Connor LLC F/B/O O’Connor Global Convertible Arbitrage Master Limited(36)			3,330,000				1.15				3,330,000				55,529				55,529				0
UBS O’Connor LLC F/B/O O’Connor Global Convertible Arbitrage II Master Limited(36)			420,000				*				420,000				7,068				7,068				0
UBS Securities LLC(5)(23)			2,600,000				*				2,600,000				43,750				43,750				0
United Technologies Corporation Master Retirement Trust(44)			438,000				*				438,000				7,370				7,370				0
Viacom Inc. Pension Plan Master Trust(44)			58,000				*				58,000				976				976				0
Vicis Capital Master Fund(13)			5,000,000				1.74				5,000,000				84,134				84,134				0
Wachovia Securities International Ltd.(5)(42)			7,500,000				2.61				7,500,000				126,200				126,200				0
Waterstone Market Neutral MAC 51, Ltd (27)			9,171,000				3.19				9,171,000				154,318				154,318				0
Waterstone Market Neutral Master Fund Ltd.(27)			15,329,000				5.33				15,329,000				257,936				257,936				0
Whitebox Diversified Convertible Arbitrage Partners L.P.(14)			1,600,000				*				1,600,000				26,923				26,923				0
Total(6)(43)		$	287,500,000				100.00	%		$	287,500,000				4,837,676				4,837,676				0

Selling security holders who are registered broker-dealers are “underwriters” within the meaning of the Securities Act of 1933. In addition, selling security holders who are affiliates of registered broker-dealers are “underwriters” within the meaning of the Securities Act of 1933 if such selling security holder (a) did not acquire its notes or underlying common stock in the ordinary course of business or (b) had an agreement or understanding, directly or indirectly, with any person to distribute the notes or underlying common stock. To our knowledge, no selling security holder who is a registered broker-dealer or an affiliate of a registered broker-dealer received any securities as underwriting compensation.

Plan of distribution

The securities to be offered and sold using this prospectus supplement are being registered to permit public secondary trading of these securities by the selling security holders from time to time after the date of this prospectus supplement. We will not receive any of the proceeds from the sale by the selling security holders of the securities offered by this prospectus supplement. The aggregate proceeds to the selling security holders from the sale of the notes or the common stock issuable upon conversion of the notes will be the purchase price of the notes less any discounts and commissions. A selling security holder reserves the right to accept and, together with its agents, to reject, any proposed purchases of notes or common stock to be made directly or through agents.

The notes and the common stock issuable upon conversion of the notes may be sold from time to time to purchasers directly by the selling security holders and their successors, which includes their transferees, pledgees or donees or their successors, or through underwriters, broker-dealers or agents who may receive compensation in the form of discounts, concessions or commissions from the selling security holders or the purchasers of the notes and the common stock issuable upon conversion of the notes. These discounts, concessions or commissions may be in excess of those customary in the types of transactions involved.

The selling security holders and any underwriters, broker-dealers or agents who participate in the distribution of the notes and the common stock issuable upon conversion of the notes may be “underwriters” within the meaning of the Securities Act of 1933, as amended, or the Securities Act. To the extent any of the selling security holders are broker-dealers, they are, under the interpretation of the SEC, “underwriters” within the meaning of the Securities Act. The following selling security holders have represented to us that it is a broker-dealer or an affiliate of a broker-dealer: Alpine Associates, Alpine Partners L.P., Canadian Imperial Holdings Inc., Citadel Equity Fund Ltd., DBAG London, D.E. Shaw Valence Portfolios, L.L.C., Fore Convertible Master Fund, Ltd., Fore Erisa Fund, Ltd., HSBC Multi Strategy Arbitrage Fund, Inflective Convertible Opportunity Fund I, Limited, Inflective Convertible Opportunity Fund I, L.P., Institutional Benchmark Series-Ivan Segregated Acct., JPMorgan Securities, KBC Financial Products USA, Inc., Lyxor/Inflective Convertible Opportunity Fund, Sunrise Partners Limited Partnership, Topaz Fund, UBS Securities LLC and Wachovia Securities International Ltd. Any profits on the sale of the notes and the common stock issuable upon the conversion of the notes by selling security holders and any discounts, commissions or concessions received by any such broker-dealers or agents may be deemed to be underwriting discounts and “underwriters” within the meaning of the Securities Act will be subject to prospectus delivery requirements of the Securities Act. If the selling security holders underwriters, the selling security holders may be subject to certain statutory liabilities of the Securities Act and the Securities Exchange Act of 1934, as amended, or the Exchange Act. We will pay all expenses of the registration of the notes and the common stock issuable under the conversion of the notes pursuant to the registration rights agreement, estimated to be $107,000 in total, including, without limitation, Securities and Exchange Commission filing fees and expenses of compliance with state securities or “blue sky” laws; provided, however, that if the notes and the common stock issuable upon conversion of the notes are sold through underwriters, broker dealers or agents, the selling security holders will be responsible for underwriting discounts or commissions or agent’s commissions.

The notes were issued and sold in June 2006 in transactions exempt from the registration requirements of the Securities Act pursuant to Rule 144A under the Securities Act. Pursuant to the registration rights agreement filed as an exhibit to the registration statement of which this prospectus is a part, we have agreed to indemnify the initial purchasers, holders who have provided us with selling securityholder questionnaires and each person, if any, who controls (within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act) the initial purchasers or the holders who have provided us with selling securityholder notices and questionnaires, from and against certain liabilities under the Securities Act or such persons will be entitled to contribution in connection with these liabilities. Pursuant to such registration rights agreement, the selling securityholders have agreed, severally and not jointly, to indemnify us and each of our directors, officers and control persons from certain liabilities under the Securities Act or we will be entitled to contribution in connection with these liabilities.