FIRST 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 First Amendment to Ground Lease  Agreement has been manually executed in
12 counterparts, numbered consecutively from 1 through 12, of which this is
No. 4.  To the extent, if any, that this First 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 First 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.


               FIRST AMENDMENT TO GROUND LEASE AGREEMENT

     This First 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 extend the lease term and to otherwise 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.  Section 5.01 of the Ground Lease Agreement is hereby amended by
deleting the reference to "April 30, 1997" and inserting in lieu thereof
"April 30, 1999".

     2.  Section 5.02 of the Ground Lease Agreement is hereby amended by
deleting the reference to "April 30, 2007" and inserting in lieu thereof
"April 30, 2009".

     3.  Section 3.02 of the Ground Lease Agreement is hereby amended to add
in the first sentence of paragraph (a) of such Section 3.02 immediately after
the words "if the terms of (b)" the additional reference to "or (c)" and to
add to such Section 3.02, a paragraph (c) which shall read as follows:  "(c)
Upon the release or disposition of a Property or any portion thereof and the
application of proceeds therefrom in accordance with Section 9.1(a)(viii) of
the Credit Agreement, Brazos and Diamond Shamrock R & M shall execute a
Revised Property Leasing Record to reflect the change in Acquisition Cost for
such Property caused by such release or disposition."

     4.  Brazos and Diamond Shamrock R & M agree that this First 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 Third Amendment and Modification Agreement by the necessary
parties under the Credit Agreement.

     5.  Defined terms used in this First 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
First 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
                                              President




                            DIAMOND SHAMROCK REFINING
                                 AND MARKETING COMPANY


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