================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
================================================================================
                             Washington, D.C. 20549
                                  -----------
                                 SCHEDULE TO/A
                                 (RULE 14D-100)

           TENDER OFFER STATEMENT UNDER SECTION 14(d)(1) or 13(e)(1)
                     OF THE SECURITIES EXCHANGE ACT OF 1934


                               (Amendment No. 8)

                              PURE RESOURCES, INC.
                           (Name of Subject Company)

                               UNOCAL CORPORATION
                        UNION OIL COMPANY OF CALIFORNIA
                       (Name of Filing Persons--Offerors)

                    COMMON STOCK, PAR VALUE $0.01 PER SHARE
                         (Title of Class of Securities)

                                  74622E 10 2
                     (CUSIP Number of Class of Securities)

                           Barry A. L. Hoffman, Esq.
                             Deputy General Counsel
                               Unocal Corporation
                       2141 Rosecrans Avenue, Suite 4000
                          El Segundo, California 90245
                                 (310) 726-7600
            (Name, Address and Telephone Number of Person Authorized
       to Receive Notices and Communications on Behalf of Filing Persons)

                                  -Copies to-
                                 Daniel A. Neff
                                Elliott V. Stein
                         Wachtell, Lipton, Rosen & Katz
                              51 West 52nd Street
                               New York, NY 10019
                                 (212) 403-1000
                                  -----------

                           CALCULATION OF FILING FEE


               Transaction Valuation*         Amount of Filing Fee
             --------------------------------------------------------
                    $501,527,875                     $46,141
             --------------------------------------------------------

*    Estimated solely for the purpose of calculating the filing fee pursuant to
     Rule 0-11 under the Securities Exchange Act of 1934, as amended, based on
     the product of (i) 22.45 the average of the high and low sales prices of
     Pure Resources, Inc.'s common stock and (ii) 23,746,505, the maximum number
     of shares to be acquired pursuant to this offer.

[X]  Check the box if any part of the fee is offset as provided by Rule
     0-11(a)(2) and identify the filing with which the offsetting fee was
     previously paid. Identify the previous filing by registration statement
     number, or the Form or Schedule and the date of its filing.
        Amount Previously Paid:  $50,916.     Filing Party:  Unocal Corporation.
        Form or Registration No.:  Form S-4.  Date Filed:  September 4, 2002
[_]  Check the box if the filing relates solely to preliminary communications
     made before the commencement of a tender offer.
Check the appropriate boxes below to designate any transactions to which the
statement relates:
[X]  third-party tender offer subject to Rule 14d-1.
[_]  issuer tender offer subject to Rule 13e-4.
[_]  going-private transaction subject to Rule 13e-3.
[X]  amendment to Schedule 13D under Rule 13d-2.
Check the following box if the filing is a final amendment reporting the results
of the tender offer: [_]
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                                  SCHEDULE 13D
------------------------                                ------------------------
 CUSIP No. 74622E 10 2                                     Page 2 of 6 Pages
--------------------------------------------------------------------------------
  1    NAME OF REPORTING PERSON
       S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Unocal Corporation
           95-3825062
--------------------------------------------------------------------------------
  2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                 (a) [ ]
                                                                        (b) [ ]
--------------------------------------------------------------------------------
  3    SEC USE ONLY

--------------------------------------------------------------------------------
  4    SOURCE OF FUNDS

           AF
--------------------------------------------------------------------------------
  5    CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
       ITEMS 2(d) or 2(e)

--------------------------------------------------------------------------------
  6    CITIZENSHIP OR PLACE OF ORGANIZATION

          Delaware
--------------------------------------------------------------------------------
    NUMBER OF      7      SOLE VOTING POWER
     SHARES
  BENEFICIALLY               -0-
   OWNED BY      ---------------------------------------------------------------
     EACH
  REPORTING        8      SHARED VOTING POWER
    PERSON
     WITH                    35,890,333(1)
--------------------------------------------------------------------------------

                   9      SOLE DISPOSITIVE POWER

                             32,709,067
--------------------------------------------------------------------------------

                  10      SHARED DISPOSITIVE POWER

                             -0-
--------------------------------------------------------------------------------
 11    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          35,890,333*
--------------------------------------------------------------------------------
 12    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN       [ ]
       SHARES

--------------------------------------------------------------------------------
 13    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

          71.3%
--------------------------------------------------------------------------------
 14    TYPE OF REPORTING PERSON

          C0
--------------------------------------------------------------------------------



--------

(1)  Includes 32,709,067 shares directly owned by Union Oil Company of
     California, and 3,181,266 shares beneficially owned by Jack D. Hightower,
     with respect to which the reporting persons may be deemed to share voting
     control by virtue of the Voting Agreement (as described on the reporting
     persons joint Statement on Schedule 13D, as amended, which is incorporated
     herein by reference).





                                  SCHEDULE 13D
------------------------                                ------------------------
 CUSIP No. 74622E 10 2                                     Page 3 of 6 Pages
--------------------------------------------------------------------------------
  1    NAME OF REPORTING PERSON
       S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Union Oil Company of California
           95-1315450
--------------------------------------------------------------------------------
  2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                 (a) [ ]
                                                                        (b) [ ]
--------------------------------------------------------------------------------
  3    SEC USE ONLY

--------------------------------------------------------------------------------
  4    SOURCE OF FUNDS

           00
--------------------------------------------------------------------------------
  5    CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
       ITEMS 2(d) or 2(e)

--------------------------------------------------------------------------------
  6    CITIZENSHIP OR PLACE OF ORGANIZATION

          California
--------------------------------------------------------------------------------
    NUMBER OF      7      SOLE VOTING POWER
     SHARES
  BENEFICIALLY               -0-
   OWNED BY      ---------------------------------------------------------------
     EACH
  REPORTING        8      SHARED VOTING POWER
    PERSON
     WITH                    35,890,333(2)
--------------------------------------------------------------------------------

                   9      SOLE DISPOSITIVE POWER

                             32,709,067
--------------------------------------------------------------------------------

                  10      SHARED DISPOSITIVE POWER

                             -0-
--------------------------------------------------------------------------------
 11    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          35,890,333*
--------------------------------------------------------------------------------
 12    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN       [ ]
       SHARES

--------------------------------------------------------------------------------
 13    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

          71.3%
--------------------------------------------------------------------------------
 14    TYPE OF REPORTING PERSON

          C0
--------------------------------------------------------------------------------



--------

(2)  Includes 32,709,067 shares directly owned by Union Oil Company of
     California, and 3,181,266 shares beneficially owned by Jack D. Hightower,
     with respect to which the reporting persons may be deemed to share voting
     control by virtue of the Voting Agreement (as described on the reporting
     persons joint Statement on Schedule 13D, as amended, which is incorporated
     herein by reference).





          This Amendment No. 8 to the Tender Offer Statement on Schedule TO and
combined Amendment No. 10 to the joint Statement on Schedule 13D (together with
the Initial Schedule TO (as defined below), as previously amended and as amended
hereby, the "Schedule TO") are filed by Unocal Corporation, a Delaware
corporation ("Unocal"), and its wholly owned subsidiary Union Oil Company of
California, a California corporation ("Union Oil", together with Unocal, the
"Reporting Persons"). The Schedule TO, amends and supplements (1) the Reporting
Persons' Tender Offer Statement on Schedule TO filed on September 4, 2002 (the
"Initial Schedule TO") and (2) the Reporting Persons' Statement on Schedule 13D,
as amended and relates to the current offer by Unocal to exchange shares of
Unocal common stock (including the associated preferred stock purchase rights)
for each outstanding share of Pure Resources, Inc. ("Pure") common stock, on the
terms and conditions contained in Unocal's prospectus, dated September 4, 2002,
as amended, and in the related letter of transmittal, copies of which are
incorporated by reference to Exhibit (a)(1), as amended, and Exhibit (a)(2) to
the Initial Schedule TO (which, together with any amendments or supplements
thereto, collectively constitute the "Offer").

ITEM 12.      EXHIBITS.

(a)(18)       Press Release of Unocal announcing the extension of the
              expiration of the Offer, dated October 23, 2002 (incorporated by
              reference to Form 425 filed by Unocal on October 23, 2002).





                                   SIGNATURE

          After due inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                        Union Oil Company of California



                                        By     /s/ Douglas M. Miller
                                          -------------------------------------
                                           Name:   Douglas M. Miller
                                           Title:  Vice President, Corporate
                                                   Development



                                        Unocal Corporation



                                        By     /s/ Douglas M. Miller
                                          -------------------------------------
                                           Name:   Douglas M. Miller
                                           Title:  Vice President, Corporate
                                                   Development




Dated:  October 23, 2002





                                 EXHIBIT INDEX



(a)(23)    Press Release of Unocal Corporation announcing the extension of the
           expiration of the Offer, dated October 23, 2002 (incorporated by
           reference to Form 425 filed by Unocal Corporation on October 23,
           2002).