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                                FIRST AMENDMENT
                                      TO
                             EMPLOYMENT AGREEMENT


         This First Amendment to the Employment Agreement (the "Amendment") is
made as of the 18th day of March, 2002 between Premcor Inc. (the "Company")
and Thomas D. O'Malley (the "Executive").

                                   RECITALS

         A. The parties hereto are parties to an Employment Agreement dated
January 30, 2002 (the "Employment Agreement").

         B. The parties hereto desire to amend and modify certain provisions of
the Employment Agreement as provided herein.


                                   AGREEMENT

         In consideration of the foregoing, the mutual covenants herein
contained and other good and valuable consideration (the receipt, adequacy and
sufficiency of which are hereby acknowledged by the parties by their execution
hereof), the parties agree as follows.

         1. Definitions. For purposes of this Amendment, capitalized terms used
herein have the same meanings ascribed to them in the Employment Agreement.

         2. Amendments to the Employment Agreement.

               2.1. Section 4 of the Employment Agreement is deleted in its
         entirety and replaced with the following:

                           "4. Annual Bonus. With respect to each fiscal year
         of the Company ending during the Employment Term, Executive shall be
         eligible to earn an annual bonus award (an "Annual Bonus") if net
         earnings per share to common shareholders of the Company, calculated
         on a fully diluted basis and according to GAAP, as determined by the
         Company's outside auditors, excluding the after-tax impact of any
         extraordinary or special items that the Board determines in good
         faith are not appropriately includable in the Annual Bonus
         calculation because such items do not accurately reflect the
         operating performance of the Company, such as inventory write ups and
         write downs, LIFO adjustments, asset purchase or sale-related gains
         or losses and acquisition-related write downs ("Adjusted EPS"), is at
         least equal to $2.50. Upon achievement of such Adjusted EPS, the
         Annual Bonus shall equal Executive's Base Salary (the "Base Bonus")
         plus, for each $0.01 increase in the applicable fiscal year's
         Adjusted EPS above $2.50 (calculated as described in the foregoing
         sentence), an amount equal to two percent of Executive's Base Salary,
         provided that in no event shall the Annual Bonus be greater than six
         times Executive's Base Salary. The Annual Bonus shall be paid to
         Executive within fifteen business days after the outside auditors
         approve the Company's year-end earnings release. The Annual Bonus for
         2002 only shall be calculated based on earnings from January 1, 2002
         and the resulting amount multiplied by 11/12ths, to arrive at the
         amount due for the eleven months of 2002, so long as Executive is


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         employed hereunder as of December 31, 2002. Annual Bonuses for
         subsequent full years during which Executive is employed hereunder
         will reflect the full year (January 1 through December 31)."

         3. No Other Modifications. Nothing herein contained in any way impairs
the Employment Agreement, or alters, waives, annuls, varies or affects any
provision, condition or covenant therein, except as specifically set forth in
this Amendment. All other provisions of the Employment Agreement remain in full
force and effect.

         4. Counterparts. This Amendment may be signed in counterparts, each of
which shall be an original, with the same effect as if the signatures thereto
and hereto were upon the same instrument.

         5. Successors; Binding Agreement. All provisions of this Amendment
shall inure to the benefit of and be binding upon personal or legal
representatives, executors, administrators, successors, heirs, distributes,
devises and legatees of the Executive.

         IN WITNESS WHEREOF, the parties hereto have duly executed this
Amendment as of the date and year first above written.

PREMCOR INC.



By:  /s/ Joseph D. Watson                          /s/ Thomas D. O'Malley
   ------------------------------------          -------------------------------
Print Name:       Joseph D. Watson               Thomas D. O'Malley
           ----------------------------
Title:     Senior Vice President and
      ---------------------------------
           Chief Administrative Officer
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