THIRD AMENDMENT

                                     TO

                         AGREEMENT FOR GROUND LEASE

                                  between

                         BRAZOS RIVER LEASING L.P.

                                    and

              DIAMOND SHAMROCK REFINING AND MARKETING COMPANY

                       Dated as of September 16, 1994
















This Third Amendment to Agreement for Ground Lease has been manually executed
in 8 counterparts, numbered consecutively from 1 through 8, of which this is
No. ____.  To the extent, if any, that this Third Amendment to Agreement for
Ground Lease constitutes chattel paper (as such term is defined in the
Uniform Commercial Code as in effect in any jurisdiction), no security
interest in this Third Amendment to Agreement for Ground Lease 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.



               THIRD AMENDMENT TO AGREEMENT FOR GROUND LEASE

This Third Amendment to Agreement for Ground Lease is made and entered into 
as of September 16, 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
an Agreement for Ground Lease, dated as of April 23, 1992 (the "Agreement for
Ground Lease"); and

    WHEREAS, Brazos and Diamond Shamrock R & M desire to amend the Agreement
for Ground Lease  to increase the permitted expenditure amount for Properties
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
acquired by Brazos under the Agreement for Ground Lease.

    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
Agreement for Ground Lease is hereby amended as follows:

     1.  Section 2.02 of the Agreement for Ground Lease is hereby amended by
deleting the reference to "$700,000" and inserting in lieu thereof
"$900,000."

     2.  Brazos and Diamond Shamrock R & M agree that this Third Amendment to
Agreement for Ground Lease 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 Amendment No. 3 to the Credit Agreement by
the necessary parties under the Credit Agreement.

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

    IN WITNESS WHEREOF, Brazos and Diamond Shamrock R & M have caused this
Third Amendment to Agreement for Ground Lease 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