Exhibit 4.1


                                                       EXECUTION COPY





                             AMENDMENT dated as of September 22,
                      1996, to the Rights Agreement dated as of
                      June 25, 1992, as amended by the First
                      Amendment dated as of October 26, 1992, and
                      the Amendment dated as of May 10, 1994 (as
                      amended, the "Rights Agreement"), by ULTRAMAR
                      CORPORATION.

          Pursuant to the terms of the Rights Agreement and in
accordance with Section 26 thereof, the following actions are
hereby taken:

          Section 1. Amendments to Rights Agreement. The Rights
Agreement is hereby amended as follows:

          (a) The definition of "Acquiring Person" in Section 1
is amended by

               (i) deleting the word "or" immediately before
          "(b)" in the first sentence of such definition and
          inserting "," in its place; and

               (ii) deleting the "." at the end of clause (y)
          after the word "occur" at the end of the first sentence
          of such definition and inserting in its place ",(c)
          Diamond Shamrock, Inc. ("DSI") or any of its
          wholly-owned subsidiaries (i) solely as a result of the
          execution and delivery of (x) the Agreement and Plan of
          Merger (the "Merger Agreement"), dated as of September
          22, 1996, between the Company and DSI or (y) the Stock
          Option Agreement (the "Option Agreement"), dated as of
          September 22, 1996, between the Company, as Issuer, and
          DSI, as Grantee, or the consummation of the
          transactions contemplated by the Merger Agreement or
          the Option Agreement, or (ii) solely as a result of DSI
          or any of its wholly-owned subsidiaries being or
          becoming the Beneficial Owner of not more than 2% of
          the Common Shares then outstanding in addition to the
          Common Shares that DSI has become the Beneficial Owner
          of as a result of the execution and delivery of the
          Option Agreement but excluding for the purposes of
          determining whether such 2% limitation has been
          exceeded Common Shares that DSI would be deemed the
          Beneficial Owner of because any DSI Benefit Plan (as
          that term is defined in the Merger Agreement) is the
          Beneficial





          Owner of such Common Shares as of the date of this
          Amendment, or (d) a Person (i) solely as a result of
          such Person taking an assignment or transfer of DSI's
          rights under the Option Agreement, in accordance with
          the terms thereof, or the consummation of the
          transactions contemplated thereby following any such
          assignment or transfer, or (ii) solely as a result of
          such Person being or becoming the Beneficial Owner of
          not more than 2% of the Common Shares then outstanding
          in addition to the Common Shares that such Person has
          become the Beneficial Owner of as a result of the
          assignment or transfer of the Option Agreement in
          accordance with its terms but excluding for the
          purposes of determining whether such 2% limitation has
          been exceeded Common Shares that such Person would be
          deemed the Beneficial Owner of because any employee
          benefit plan of such Person is the Beneficial Owner of
          such Common Shares as of the date of such assignment or
          transfer."

          (b) A new Section 33 is added as follows:

          "Section 33. Merger with DSI. Notwithstanding any
     provision herein to the contrary, (i) neither DSI nor any of
     its wholly-owned subsidiaries shall be considered an
     Acquiring Person under this Rights Agreement, no
     Distribution Date shall occur, and no Rights shall be
     exercisable pursuant to Section 7, Section 11 or any other
     provision hereof, (x) solely as a result of the approval,
     execution or delivery of the Merger Agreement or the Option
     Agreement or the consummation of the transactions
     contemplated by the Merger Agreement or the Option
     Agreement, or (y) solely as a result of DSI or any of its
     wholly- owned subsidiaries being or becoming the Beneficial
     Owner of not more than 2% of the Common Shares then
     outstanding in addition to the Common Shares that DSI has
     become the Beneficial Owner of as a result of the execution
     and delivery of the Option Agreement but excluding for the
     purposes of determining whether such 2% limitation has been
     exceeded Common Shares that DSI would be deemed the
     Beneficial Owner of because any DSI Benefit Plan (as that
     term is defined in the Merger Agreement) is the Beneficial
     Owner of such Common Shares as of the date of this
     Amendment, and (ii) no Person shall be considered an
     Acquiring Person under this Rights Agreement, no
     Distribution Date shall





     occur, and no Rights shall be exercisable pursuant to
     Section 7, Section 11 or any other provision hereof, (x)
     solely as a result of such Person taking an assignment or
     transfer of DSI's rights under the Option agreement, in
     accordance with the terms thereof, or the consummation of
     the transactions contemplated thereby following any such
     assignment or transfer, or (y) solely as a result of such
     Person being or becoming the Beneficial Owner of not more
     than 2% of the Common Shares then outstanding in addition to
     the Common Shares that such Person has become the Beneficial
     Owner of as a result of the assignment or transfer of the
     Option Agreement in accordance with its terms but excluding
     for the purposes of determining whether such 2% limitation
     has been exceeded Common Shares that such Person would be
     deemed the beneficial Owner of because any employee benefit
     plan of such Person is the Beneficial Owner of such Common
     Shares as of the date of such assignment or transfer."

          Section 2. Full Force and Effect. Except as expressly
amended hereby, the Rights Agreement shall continue in full force
and effect in accordance with the provisions thereof on the date
hereof.

          Section 3. Governing Law. This Amendment shall be
governed by and construed in accordance with the law of the State
of Delaware applicable to contracts to be made and performed
entirely within such State.


          IN WITNESS WHEREOF, the Company has caused this
Amendment to be duly executed as of the day and year first above
written.

                                    ULTRAMAR CORPORATION,


                                    By: /s/ Patrick J. Guarino
                                       ------------------------------
                                       Name:  Patrick J. Guarino
                                       Title: Vice President, General
                                              Counsel and Secretary