Exhibit 10.1


                              SECOND AMENDMENT
  
                                     TO

                           GROUND LEASE AGREEMENT

                                  between

                          BRAZOS RIVER LEASING L.P.

                                    and

               DIAMOND SHAMROCK REFINING AND MARKETING COMPANY

                          Dated as of June 1, 1994




This Second Amendment to Ground Lease Agreement has been manually executed in 12
counterparts, numbered consecutively from 1 through 12, of which this is No.
____.  To the extent, if any, that this Second Amendment to Ground Lease
Agreement constitutes chattel paper (as such term is defined in the Uniform
Commercial Code as in effect in any jurisdiction), no security interest in this
Second Amendment to Ground Lease Agreement may be created or perfected through
the transfer or possession of any counterpart other than the original
counterpart which shall be the counterpart identified as counterpart No. 1.

                 SECOND AMENDMENT TO GROUND LEASE AGREEMENT

     This Second Amendment to Ground Lease Agreement is made and entered into as
of June 1, 1994, by and between BRAZOS RIVER LEASING L.P. ("Brazos") and DIAMOND
SHAMROCK REFINING AND MARKETING COMPANY ("Diamond Shamrock R & M").

                        W I T N E S S E T H:

     WHEREAS, Brazos and Diamond Shamrock R & M have heretofore entered into a
Ground Lease Agreement, dated as of October 30, 1992 (the "Ground Lease
Agreement"); and 

     WHEREAS, Brazos and Diamond Shamrock R & M desire to amend the Ground Lease
Agreement to set forth their mutual agreement; and 

     WHEREAS, Brazos and Diamond Shamrock R & M agree that the provisions of
this amendment shall apply, to the extent provided by law, to each Property
leased by Brazos under the Ground Lease Agreement.

     NOW, THEREFORE, in consideration of the mutual covenants herein contained
and other valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, Brazos and Diamond Shamrock R & M agree that the Ground
Lease Agreement is hereby amended as follows:

     1.  The definition of "Basic Rent" in Section 1.01 of the Ground Lease
Agreement is hereby amended to delete from paragraph (iii) thereof the reference
to "0.95%" and insert in lieu thereof "0.20%".  

     2.  Brazos and Diamond Shamrock R & M agree that this Second Amendment to
Ground Lease Agreement shall not be effective until the approvals required by
Section 9.01 of the Credit Agreement have been obtained as evidenced by the
execution of the Fourth Amendment and Modification Agreement by the necessary
parties under the Credit Agreement.

     3.  Defined terms used in this Second Amendment to Ground Lease Agreement
and not otherwise defined herein have the meanings ascribed to those terms in
the Ground Lease Agreement. 

     IN WITNESS WHEREOF, Brazos and Diamond Shamrock R & M have caused this
Second Amendment to Ground Lease Agreement to be executed and delivered by their
duly authorized officers as of the day and year first above written.


                             BRAZOS RIVER LEASING L.P.

                             By:  Headwater Investments L.P.,
                                  its General Partner

                                  By: Headwater Holdings, Inc.,
                                      its General Partner


                                  By: /S/ GREGORY C. GREENE
                                          Gregory C. Greene,
                                          President



                             DIAMOND SHAMROCK REFINING
                                  AND MARKETING COMPANY


                             By: /S/ R.C. BECKER
                             Name:   R.C. Becker
                             Title:  Vice President and Treasurer


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