EXHIBIT 24.2

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned, on behalf of Ultramar
Diamond Shamrock Corporation, a Delaware corporation (the "Corporation"), hereby
constitutes  and  appoints  Timothy  J.  Fretthold,  H.  Pete  Smith,  Curtis V.
Anastasio,  and Todd Walker,  attorneys-in-fact  and agents of the  Corporation,
with full power of substitution and  resubstitution,  to do any and all acts and
things in its name and on its behalf and to execute any and all  instruments  in
its name in such capacity which they may deem appropriate or advisable to enable
the Corporation to comply with the Securities  Exchange Act of 1934, as amended,
and any rules and  regulations  of the Securities  and Exchange  Commission,  in
connection with the Corporation's Annual Report on Form 10-K for the fiscal year
ended December 31, 1997,  including without  limitation,  the power to sign such
report on the Corporation's  behalf and to sign any amendments  thereto,  and to
file the same,  with all  exhibits  thereto,  and other  documents  required  in
connection therewith,  with the Securities and Exchange Commission,  granting to
each and all of said  attorneys-in-fact,  full  power  and  authority  to do and
perform  each and every  act and thing  requisite  and  necessary  to be done in
connection with the filing of such report as herein described.

ULTRAMAR DIAMOND SHAMROCK CORPORATION



/s/ R. R. HEMMINGHAUS
    R. R. Hemminghaus
    Chairman of the Board and
    Chief Executive Officer

Dated: February 4, 1998