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. 1)

                              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
                  ----------------------   --------------------
                                        
                       $553,431,082               $50,916


*    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) 23.20 the average of the high and low sales prices of
     Pure Resources, Inc.'s common stock and (ii) 23,854,788, 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: [ ]









                                  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          8     SHARED VOTING POWER
   REPORTING
     PERSON                 35,890,333(1)
      WITH
                    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           8    SHARED VOTING POWER
   REPORTING
     PERSON                  35,890,333(2)
      WITH
                     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. 1 to the Tender Offer Statement on Schedule TO
and combined Amendment No. 3 to the joint Statement on Schedule 13D (together
with the Initial Schedule TO (as defined below) 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 offer by Unocal to exchange 0.6527 of a share of
Unocal common stock (including the associated preferred stock purchase rights)
for each outstanding share of Pure Resources, Inc. 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) hereof and Exhibit (a)(2) to the
Initial Schedule TO (which, together with any amendments or supplements thereto,
collectively constitute the "Offer").

ITEMS 1 TO 11.

            The information set forth in the Offer is incorporated herein by
reference with respect to Items 1-11 of this Schedule TO.

ITEM 12.    EXHIBITS.

(a)(1)      Prospectus dated September 4, 2002 (incorporated by reference from
            Unocal's Registration Statement on Form S-4 filed with the SEC on
            September 4, 2002, as amended by Amendment No. 1 to the Registration
            Statement on Form S-4 filed with the SEC on September 5, 2002 (as
            amended, the "Form S-4")).

(a)(5)      Press Release of Unocal announcing the commencement of the Offer,
            dated September 5, 2002 (incorporated by reference to Form 425 filed
            by Unocal on September 5, 2002).


ITEM 13.    INFORMATION REQUIRED BY SCHEDULE 13E-3.

            Not applicable






                                    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:  September 6, 2002






                                  EXHIBIT INDEX




         
(a)(1)      Prospectus dated September 4, 2002 (incorporated by reference from
            Unocal Corporation's Registration Statement on Form S-4 filed with
            the SEC on September 4, 2002, as amended by Amendment No. 1 to the
            Registration Statement on Form S-4 filed with the SEC on September
            5, 2002 (the "Form S-4")).

(a)(5)      Press Release of Unocal Corporation announcing commencement of the
            offer, dated September 5, 2002 (incorporated by reference to Form
            425 filed by Unocal on September 5, 2002).