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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                ----------------

                                  SCHEDULE 13D
             INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
     TO RULE 13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO RULE 13d-2(a)

                                (AMENDMENT NO. 6)

                                ----------------


                              PLAINS RESOURCES INC.

                                (Name of Issuer)

COMMON STOCK, PAR VALUE $.10 PER SHARE                   726540503
--------------------------------------    --------------------------------------
   (Title of class of securities)                     (CUSIP number)

JOSEPH A. ORLANDO                     WILLIAM ACKMAN
LEUCADIA NATIONAL CORPORATION         PERSHING SQUARE CAPITAL MANAGEMENT, L.P.
315 PARK AVENUE SOUTH                 110 EAST 42ND STREET
NEW YORK, NEW YORK 10010              NEW YORK, NEW YORK  10017
(212) 460-1900                        (212) 813-3700
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            (Name, address and telephone number of person authorized
                     to receive notices and communications)

                                  MAY 26, 2004
--------------------------------------------------------------------------------
             (Date of event which requires filing of this statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of Rules 13d-1(e), 13d-1(f) or 13d-1(g), check the following
box [_].


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------------------------------------------------------------       -----------------------------------------------------------------
CUSIP NO. 726540503                                           13D                                                  Page 2
------------------------------------------------------------       -----------------------------------------------------------------
                                                                                                       
-------------- ---------------------------------------- --------------------------------------------------------------------------
      1        NAME OF REPORTING PERSON:                Leucadia National Corporation
               I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):
-------------- ----------------------------------------------------------------------------------------------------- -------------
      2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                                          (A) [X]
                                                                                                                          (B) [_]
-------------- -------------------------------------------------------------------------------------------------------------------
      3        SEC USE ONLY

-------------- ----------------------- -------------------------------------------------------------------------------------------
      4        SOURCE OF FUNDS:        NA

-------------- ----------------------------------------------------------------------------------------------------- -------------
      5        CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e):                        [_]
-------------- ----------------------------------------------------- -------------------------------------------------------------
      6        CITIZENSHIP OR PLACE OF ORGANIZATION:                 New York

----------------------- ----- -------------------------------------- -------------------------------------------------------------
      NUMBER OF          7    SOLE VOTING POWER:                     0
        SHARES
                        ----- -------------------------------------- -------------------------------------------------------------
     BENEFICIALLY        8    SHARED VOTING POWER:                   0
       OWNED BY
                        ----- -------------------------------------- -------------------------------------------------------------
         EACH            9    SOLE DISPOSITIVE POWER:                0
      REPORTING
                        ----- -------------------------------------- -------------------------------------------------------------
     PERSON WITH         10   SHARED DISPOSITIVE POWER:              0

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

-------------- ----------------------------------------------------------------------------------------------------- -------------
     12        CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                                         [_]

-------------- -------------------------------------------------------------------------------------------------------------------
     13        PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):   0%

-------------- ---------------------------------------- --------------------------------------------------------------------------
     14        TYPE OF REPORTING PERSON:                CO

-------------- ---------------------------------------- --------------------------------------------------------------------------


                                       2

------------------------------------------------------------       -----------------------------------------------------------------
CUSIP NO. 726540503                                           13D                                                  Page 3
------------------------------------------------------------       -----------------------------------------------------------------

-------------- ---------------------------------------- --------------------------------------------------------------------------
      1        NAME OF REPORTING PERSON:                Pershing Square, L.P.
               I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):   38-3694138
-------------- ----------------------------------------------------------------------------------------------------- -------------
      2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                                          (A) [X]
                                                                                                                          (B) [_]
-------------- -------------------------------------------------------------------------------------------------------------------
      3        SEC USE ONLY

-------------- ----------------------- -------------------------------------------------------------------------------------------
      4        SOURCE OF FUNDS:        NA

-------------- ----------------------------------------------------------------------------------------------------- -------------
      5        CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e):                        [_]
-------------- ----------------------------------------------------- -------------------------------------------------------------
      6        CITIZENSHIP OR PLACE OF ORGANIZATION:                 Delaware

----------------------- ----- -------------------------------------- -------------------------------------------------------------
      NUMBER OF          7    SOLE VOTING POWER:                     0
        SHARES
                        ----- -------------------------------------- -------------------------------------------------------------
     BENEFICIALLY        8    SHARED VOTING POWER:                   1,258,500
       OWNED BY
                        ----- -------------------------------------- -------------------------------------------------------------
         EACH            9    SOLE DISPOSITIVE POWER:                0
      REPORTING
                        ----- -------------------------------------- -------------------------------------------------------------
     PERSON WITH         10   SHARED DISPOSITIVE POWER:              1,258,500

-------------- -------------------------------------------------------------------------------------------------------------------
     11        AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:   1,258,500

-------------- ----------------------------------------------------------------------------------------------------- -------------
     12        CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                                         [_]

-------------- -------------------------------------------------------------------------------------------------------------------
     13        PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):   5.33%

-------------- ---------------------------------------- --------------------------------------------------------------------------
     14        TYPE OF REPORTING PERSON:                PN

-------------- ---------------------------------------- --------------------------------------------------------------------------


                                       3

------------------------------------------------------------       -----------------------------------------------------------------
CUSIP NO. 726540503                                           13D                                                  Page 4
------------------------------------------------------------       -----------------------------------------------------------------

-------------- ---------------------------------------- --------------------------------------------------------------------------
      1        NAME OF REPORTING PERSON:                         Pershing Square GP, LLC
               I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):   38-3694141
-------------- ----------------------------------------------------------------------------------------------------- -------------
      2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                                          (A) [X]
                                                                                                                          (B) [_]
-------------- -------------------------------------------------------------------------------------------------------------------
      3        SEC USE ONLY

-------------- ----------------------- -------------------------------------------------------------------------------------------
      4        SOURCE OF FUNDS:        N/A

-------------- ----------------------------------------------------------------------------------------------------- -------------
      5        CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e):                        [_]
-------------- ----------------------------------------------------- -------------------------------------------------------------
      6        CITIZENSHIP OR PLACE OF ORGANIZATION:                 Delaware

----------------------- ----- -------------------------------------- -------------------------------------------------------------
      NUMBER OF          7    SOLE VOTING POWER:                     0
        SHARES
                        ----- -------------------------------------- -------------------------------------------------------------
     BENEFICIALLY        8    SHARED VOTING POWER:                   1,258,500
       OWNED BY
                        ----- -------------------------------------- -------------------------------------------------------------
         EACH            9    SOLE DISPOSITIVE POWER:                0
      REPORTING
                        ----- -------------------------------------- -------------------------------------------------------------
     PERSON WITH         10   SHARED DISPOSITIVE POWER:              1,258,500

-------------- -------------------------------------------------------------------------------------------------------------------
     11        AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:   1,258,500
-------------- ----------------------------------------------------------------------------------------------------- -------------
     12        CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                                         [_]

-------------- -------------------------------------------------------------------------------------------------------------------
     13        PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):   5.33%

-------------- ---------------------------------------- --------------------------------------------------------------------------
     14        TYPE OF REPORTING PERSON:                OO

-------------- ---------------------------------------- --------------------------------------------------------------------------


                                       4

------------------------------------------------------------       -----------------------------------------------------------------
CUSIP NO. 726540503                                           13D                                                  Page 5
------------------------------------------------------------       -----------------------------------------------------------------

-------------- ---------------------------------------- --------------------------------------------------------------------------
      1        NAME OF REPORTING PERSON:                         William Ackman
               I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):
-------------- ----------------------------------------------------------------------------------------------------- -------------
      2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                                          (A) [X]
                                                                                                                          (B) [_]
-------------- -------------------------------------------------------------------------------------------------------------------
      3        SEC USE ONLY

-------------- ----------------------- -------------------------------------------------------------------------------------------
      4        SOURCE OF FUNDS:        N/A

-------------- ----------------------------------------------------------------------------------------------------- -------------
      5        CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e):                        [_]
-------------- ----------------------------------------------------- -------------------------------------------------------------
      6        CITIZENSHIP OR PLACE OF ORGANIZATION:                 United States

----------------------- ----- -------------------------------------- -------------------------------------------------------------
      NUMBER OF          7    SOLE VOTING POWER:                     0
        SHARES
                        ----- -------------------------------------- -------------------------------------------------------------
     BENEFICIALLY        8    SHARED VOTING POWER:                   1,258,500
       OWNED BY
                        ----- -------------------------------------- -------------------------------------------------------------
         EACH            9    SOLE DISPOSITIVE POWER:                0
      REPORTING
                        ----- -------------------------------------- -------------------------------------------------------------
     PERSON WITH         10   SHARED DISPOSITIVE POWER:              1,258,500

-------------- -------------------------------------------------------------------------------------------------------------------
     11        AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:   1,258,500

-------------- ----------------------------------------------------------------------------------------------------- -------------
     12        CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                                         [_]

-------------- -------------------------------------------------------------------------------------------------------------------
     13        PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):   5.33%

-------------- ---------------------------------------- --------------------------------------------------------------------------
     14        TYPE OF REPORTING PERSON:                IN

-------------- ---------------------------------------- --------------------------------------------------------------------------



                                       5

           This Amendment No. 6 amends the Schedule 13D filed on February 23,
2004, and is filed by Leucadia National Corporation ("Leucadia"), Pershing
Square, L.P., Pershing Square GP, LLC and William Ackman (collectively, the
"Reporting Persons") with respect to the common stock, par value $0.10 per share
("Common Stock"), of Plains Resources Inc. (the "Company").

Item 4.    Purpose of Transaction.
           ----------------------

           Item 4 is hereby supplemented as follows:

           On May 12, 2004, representatives of the special committee of the
Company's Board of Directors requested that Leucadia substantially improve the
economics of its current proposal (the "Proposal") to acquire the Company in
exchange for a package of debt (rated B2 by Moody's Investors Service),
preferred stock and cash. Among other things, the special committee requested
that Leucadia (i) increase the cash offered to $150 million, (ii) increase the
yield on the notes by $0.16 per annum and (iii) eliminate the preferred stock
and tender offer components of the Proposal.

           Leucadia believes that the Proposal is superior to the current $16.75
per share proposed transaction and remains committed to the Proposal. In view of
the special committee's request, Leucadia did not believe that a meeting with
the special committee was warranted.

           The Reporting Persons may acquire additional securities of the
Company or dispose of securities of the Company at any time and from time to
time in the open market, in privately negotiated transactions or otherwise.

           Although the foregoing represents the range of activities presently
contemplated by the Reporting Persons and, to their knowledge, their respective
general partners, directors and officers, as applicable, with respect to the
Company, it should be noted that the possible activities of the Reporting
Persons and their respective general partners, directors and officers are
subject to change at any time.


Item 7.    Materials to be Filed as Exhibits.
           ---------------------------------

1. Agreement among the Reporting Persons with respect to the filing of this
Schedule 13D.




                                       6

                                    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.

                                        LEUCADIA NATIONAL CORPORATION


                                        By:   /s/ Joseph A. Orlando
                                            ------------------------------------
                                            Name:  Joseph A. Orlando
                                            Title: Vice President and Chief
                                                   Financial Officer


                                        PERSHING SQUARE, L.P.

                                        By:    PERSHING SQUARE GP, LLC


                                        By:   /s/ William Ackman
                                            ------------------------------------
                                            Name:  William Ackman
                                            Title: Managing Member



                                        PERSHING SQUARE GP, LLC


                                        By:   /s/ William Ackman
                                            ------------------------------------
                                            Name:  William Ackman
                                            Title: Managing Member



                                        By:   /s/ William Ackman
                                            ------------------------------------
                                            Name: William Ackman






Date:    May 26, 2004



                                       7

                                  EXHIBIT INDEX
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Exhibit No.
-----------

Exhibit 1 -    Agreement among the Reporting Persons with respect to the filing
               of this Schedule 13D.











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