UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934

                             (AMENDMENT NO. __3__)*

                                   Unocal Corp
-------------------------------------------------------------------------------
                                (Name of Issuer)

                                     Common
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    915289102
                  -------------------------------------------
                                 (CUSIP Number)

                                December 31, 2003
         --------------------------------------------------------------
             (Date of Event Which Requires Filing of this Statement)


Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

[X] Rule 13d-1(b)
[_] Rule 13d-1(c)
[_] Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

                                PAGE 1 OF 4 PAGES



-------------------------                                  ---------------------
  CUSIP NO.915289102                     13G                 PAGE 2 OF 4 PAGES
-------------------------                                  ---------------------

--------------------------------------------------------------------------------
 1     NAME OF REPORTING PERSON
       S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

       Dodge & Cox                    94-1441976
--------------------------------------------------------------------------------
 2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*          (a) [_]
                                                                  (b) [_]

       N/A
--------------------------------------------------------------------------------
 3     SEC USE ONLY

--------------------------------------------------------------------------------
 4     CITIZENSHIP OR PLACE OF ORGANIZATION

       California - U.S.A.
--------------------------------------------------------------------------------
                     5    SOLE VOTING POWER

     NUMBER OF            26,134,744
      SHARES       -------------------------------------------------------------
                     6    SHARED VOTING POWER
   BENEFICIALLY
     OWNED BY             269,300
                   -------------------------------------------------------------
       EACH          7    SOLE DISPOSITIVE POWER

    REPORTING             27,901,694
      PERSON       -------------------------------------------------------------
                     8    SHARED DISPOSITIVE POWER
       WITH
                          0
--------------------------------------------------------------------------------
 9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

       27,901,694
--------------------------------------------------------------------------------
10     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

       N/A
--------------------------------------------------------------------------------
11     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

       10.8%
--------------------------------------------------------------------------------
12     TYPE OF REPORTING PERSON*

       IA
--------------------------------------------------------------------------------



       Item 1(a) Name of Issuer:
                 Unocal Corp

       Item 1(b) Address of Issuer's Principal Executive Offices:
                 2141 Rosecrans Avenue, Suite 4000
                 El Segundo, CA 90245

       Item 2(a) Name of Person Filing:
                 Dodge & Cox

       Item 2(b) Address of the Principal Office or, if none, Residence:
                 One Sansome St., 35th Floor
                 San Francisco, CA 94104

       Item 2(c) Citizenship:
                 California - U.S.A.

       Item 2(d) Title of Class of Securities:
                 Common

       Item 2(e) CUSIP Number:
                 915289102

       Item 3    If the Statement is being filed pursuant to Rule 13d-1(b), or
                 13d-2(b), check whether the person filing is a:

                 (e) [X] Investment Advisor registered under section 203 of the
                         Investment Advisors Act of 1940

       Item 4    Ownership:
                 (a) Amount Beneficially Owned:
                     27,901,694

                 (b) Percent of Class:
                     10.8%

                             PAGE 3 OF 4 PAGES



                 (c) Number of shares as to which such person has:

                 (i) sole power to vote or direct the vote: 26,134,744

                (ii) shared power to vote or direct the vote: 269,300

               (iii) sole power to dispose or to direct the disposition of:
                     27,901,694

                (iv) shared power to dispose or to direct the disposition of: 0

       Item 5    Ownership of Five Percent or Less of a Class:
                 Not applicable.

       Item 6    Ownership of More than Five Percent on Behalf of Another
                 Person:

                 Securities reported on this Schedule 13G are beneficially owned
                 by clients of Dodge & Cox, which clients may include investment
                 companies registered under the Investment Company Act and/or
                 employee benefit plans, pension funds, endowment funds or other
                 institutional clients.

       Item 7    Identification and Classification of the Subsidiary Which
                 Acquired the Security Being Reported on By the Parent Holding
                 Company:
                 Not applicable.

       Item 8    Identification and Classification of Members of the Group:
                 Not applicable.

       Item 9    Notice of Dissolution of a Group:
                 Not applicable.

       Item 10   Certification:
                 By signing below I certify that, to the best of my knowledge
                 and belief, the securities referred to above were acquired in
                 the ordinary course of business and were not acquired for the
                 purpose of and do not have the effect of changing or
                 influencing the control of the issuer of such securities and
                 were not acquired in connection with or as a participant in
                 any transaction having such purpose or effect.

                                    SIGNATURE

       After reasonable 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.

Dated:  February 17, 2004

                                      DODGE & COX

                                      By:    /S/ THOMAS M. MISTELE
                                         ---------------------------------------
                                      Name:  Thomas M. Mistele
                                      Title: Vice President

                                PAGE 4 OF 4 PAGES