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                                                                   EXHIBIT 10.23

                               AMENDMENT TO THE
                         CLARK RETIREMENT SAVINGS PLAN


     This Plan Amendment, executed on the 30th day of December, 1999, by Clark
Refining & Marketing, Inc., a Delaware corporation ("Company").

                                  WITNESSETH
                                  ----------

     WHEREAS, Clark Refining & Marketing, Inc., a Delaware corporation
established a 401(k)/profit sharing plan, the Clark Retirement Savings Plan (the
"Plan') effective January 1, 1989; and

     WHEREAS, the Company adopted an amended and restated Plan document
effective April 1, 1994 (the "Amended and Restated Plan"); and

     WHEREAS, the Company amended the Amended and Restated Plan effective
October 31, 1997, December 21, 1998 and July 6, 1999 by Board of Directors
Resolutions; and

     WHEREAS, the Company desires to further amend the Amended and Restated Plan
by the adoption of this Amendment to the Plan.

     NOW, THEREFORE, the Company amends the Amended and Restated Plan as
follows:

     1.   Effective for all Plan Years beginning on or after January 1,1999,
          Section 5.1 shall be deleted in its entirety and substituted in lieu
          thereof is the following:

          5.1.  Matching Contributions.  Subject to the conditions and
                ----------------------
                limitations of Section 8, for each Plan Year an Employer shall
                contribute to the Plan on behalf of each Participant employed by
                such Employer an amount equal to 200 percent of the Before-Tax
                Contributions made on behalf of the Participant that do not
                exceed 3 percent of such Participant's Eligible Compensation for
                such Plan Year. Any contribution made pursuant to this
                subsection 5.1 shall be referred to hereinafter as a "Matching
                Contribution". At all times, Matching Contributions made with
                respect to Participants who are not Union Participants shall be
                made in a manner to qualify under the safe harbor rules of
                Section 401(k)(10) of the Code.

     2.   Effective for all Plan Years beginning on or after January 1, 1999,
          Section 5.2 is deleted in its entirety.
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     3.   Effective with all Plan Years beginning on or after January 1, 1999,
          Section 9.1 is deleted in its entirety and substituted in lieu thereof
          is the following:

          9.1    Determination of Vested Interest.  The interest of a Union
                 --------------------------------
                 Participant in his Matching Account shall become fully vested
                 and nonforfeitable in accordance with the following schedule:

                  Years of Service              Vested Percentage
                  ----------------              -----------------
                  Fewer than 1                         0
                  1 but fewer than 2                   20
                  2 but fewer than 3                   40
                  3 but fewer than 4                   60
                  4 but fewer than 5                   80
                  5 or more                           100

                 A Union Participant shall at all times have a nonforfeitable
                 interest in his Before-Tax Account, After-Tax Account and
                 Rollover Account.

                 A Participant who is not a Union Participant shall at all times
                 have a nonforfeitable interest in his Before-Tax Account,
                 After-Tax Account, Rollover Account and Matching Account.

     4.   Sections 10.1(a) and (b) are deleted in their entirety and substituted
          in lieu thereof are the following:

          10.1.  Loans to Participants.  For Plan Years beginning on or after
                 ---------------------
                 January 1, 1997 and prior to January 1, 2000, the Committee,
                 upon request by a Participant who is an employee of an Employer
                 or a Related Company, or who is otherwise required to be given
                 the opportunity to borrow under applicable regulations, in such
                 form as the Committee may require, may, to the extent required
                 under applicable law or regulations, authorize a loan to be
                 made to the Participant from all his Accounts, subject to the
                 following:

                 (a)  No loan shall be made to a Participant if, immediately
                      after such loan, the sum of the outstanding balances
                      (including principal and interest) of all loans made to
                      him under this Plan and under any other qualified
                      retirement plans maintained by the Related Companies would
                      exceed the lesser of:

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                      (i)  $50,000 reduced by the excess, if any, of:

                           (A)  the highest outstanding balance of all loans to
                                the Participant from the plans during the one-
                                year period ending on the day immediately before
                                the date on which the loan is made; over

                           (B)  the outstanding balance of loans from the plans
                                to the Participant on the date on which such
                                loan is made; or

                      (ii) the lesser of one-half of the total vested balance of
                           the Participant's Accounts under the Plan as of the
                           date the loan is made.

                 (b)  Each loan to a Participant shall be charged pro rata
                      against the Participant's Accounts and shall be charged
                      against each Investment Fund in which his Accounts are
                      invested in the same ratio as the value of his interest in
                      such fund with respect to each such Account bears to the
                      total of all his interest in that Account.

                 For Plan Years beginning before January 1, 1997 and on or after
                 January 1, 2000, the Committee, upon request by a Participant
                 who is an employee of an Employer or a Related Company, or who
                 is otherwise required to be given the opportunity to borrow
                 under applicable regulations, in such form as the Committee may
                 require, may, to the extent required under applicable law or
                 regulations, authorize a loan to be made to the Participant
                 from his Before-Tax Account, subject to the following:

                 (aa) No loan shall be made to a Participant if, immediately
                      after such loan, the sum of the outstanding balances
                      (including principal and interest) of all loans made to
                      him under this Plan and under any other qualified
                      retirement plans maintained by the Related Companies would
                      exceed the lesser of:

                      (i)  $50,000 reduced by the excess, if any, of:
                           (A)  the highest outstanding balance of all loans to
                                the Participant from the plans during the one-
                                year period ending on the

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                                day immediately before the date on which the
                                loan is made; over

                           (B)  the outstanding balance of loans from the plans
                                to the Participant on the date on which such
                                loan is made; or

                      (ii) the lesser of one-half of the total vested balance of
                           the Participant's Accounts under the Plan as of the
                           date the loan is made or the balance in the
                           Participant's Before-Tax Account.

                 (bb) Each loan to a Participant shall be charged against the
                      Participant's Before-Tax Account and shall be charged
                      against each Investment Fund in which his Before-Tax
                      Account is invested in the same ratio as the value of his
                      interest in such Fund with respect to the Before-Tax
                      Account bears to the total of all his interest in that
                      Account.

     5.   Section 11.15 is added as follows:

          11.15  Account Transfer - Acquired Employees: Effective for the Plan
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                 Year beginning on or after January 1, 2000; Accounts of
                 Participants who are "Acquired Employees", as that term is
                 defined in the Asset Purchase Agreement by and between Clark
                 Refining & Marketing, Inc. and Equilon Enterprises LLC dated as
                 of December 1, 1999 ("Transaction"), shall be transferred to a
                 qualified plan maintained by the purchaser in such transaction.
                 As such Transaction is expected to close during the Plan Year
                 beginning January 1, 2000; the transfer of Accounts shall occur
                 as soon as administratively practicable following the closing
                 of the Transaction.

     6.   A new A-14 is added to Supplement A as follows:

          Union Participant  A-14.  A Union Participant shall mean a Participant
          -----------------
                             who is a member of a collective bargaining unit as
                             to which retirement benefits have been the subject
                             of good faith bargaining.

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     IN WITNESS WHEREOF, the Company has caused this Plan amendment to be
executed on the day and year first above written.

                            CLARK REFINING & MARKETING, INC.



                            By:______________________________________________
                                 Maura J. Clark
                                 Executive Vice President and Chief Financial
                                 Officer

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