POWER OF ATTORNEY


         KNOW ALL  MEN BY THESE  PRESENTS, that  I, the  undersigned,  do hereby
constitute and appoint Susan S. Keith, John M. Allen and Bruce A. Metzinger,  or
any of them acting alone, my true and lawful  attorneys-in-fact and agents, with
full power of substitution and  resubstitution,  to prepare and sign for me, and
in my name,  place and stead, in any and all capacities,  any and all reports as
may from time to time be required under Section 16(a) of the Securities Exchange
Act of 1934, as amended,  and the rules,  regulations  and  requirements  of the
Securities and Exchange Commission in respect thereof, and to file the same with
the Securities and Exchange Commission, granting unto said attorneys-in-fact and
agents full power and  authority  to do and perform each and every act and thing
requisite  and  necessary  to be done  (with  full  power to each of them to act
alone),  as fully  and to all  intents  and  purposes  as I might or could do in
person,  hereby  ratifying and  confirming all that said  attorneys-in-fact  and
agents or any of them, or their substitutes, may lawfully do or cause to be done
by virtue hereof.
         This Power of  Attorney shall  remain in  full force  and  effect until
revoked by me in writing.
         IN WITNESS WHEREOF, I hereto set my hand this 21st day of May, 2001.

                                       /s/ Kenneth T. Derr
                                       -----------------------------------------
                                           Kenneth T. Derr



                                POWER OF ATTORNEY


         KNOW ALL  MEN BY  THESE PRESENTS, that  I,  the undersigned,  do hereby
constitute and appoint Susan S. Keith, John M. Allen and Bruce A. Metzinger,  or
any of them acting alone, my true and lawful  attorneys-in-fact and agents, with
full power of substitution and  resubstitution,  to prepare and sign for me, and
in my name,  place and stead, in any and all capacities,  any and all reports as
may from time to time be required under Section 16(a) of the Securities Exchange
Act of 1934, as amended,  and the rules,  regulations  and  requirements  of the
Securities and Exchange Commission in respect thereof, and to file the same with
the Securities and Exchange Commission, granting unto said attorneys-in-fact and
agents full power and  authority  to do and perform each and every act and thing
requisite  and  necessary  to be done  (with  full  power to each of them to act
alone),  as fully  and to all  intents  and  purposes  as I might or could do in
person,  hereby  ratifying and  confirming all that said  attorneys-in-fact  and
agents or any of them, or their substitutes, may lawfully do or cause to be done
by virtue hereof.
         This Power of Attorney  shall remain in  full force  and  effect  until
revoked by me in writing.
         IN WITNESS WHEREOF, I hereto set my hand this 15th day of May, 2001.

                                       /s/ Aylwin B. Lewis
                                       -----------------------------------------
                                           Aylwin B. Lewis



                                POWER OF ATTORNEY


         KNOW ALL MEN BY  THESE PRESENTS, that  I, the  undersigned,  do  hereby
constitute and appoint Susan S. Keith, John M. Allen and Bruce A. Metzinger,  or
any of them acting alone, my true and lawful  attorneys-in-fact and agents, with
full power of substitution and  resubstitution,  to prepare and sign for me, and
in my name,  place and stead, in any and all capacities,  any and all reports as
may from time to time be required under Section 16(a) of the Securities Exchange
Act of 1934, as amended,  and the rules,  regulations  and  requirements  of the
Securities and Exchange Commission in respect thereof, and to file the same with
the Securities and Exchange Commission, granting unto said attorneys-in-fact and
agents full power and  authority  to do and perform each and every act and thing
requisite  and  necessary  to be done  (with  full  power to each of them to act
alone),  as fully  and to all  intents  and  purposes  as I might or could do in
person,  hereby  ratifying and  confirming all that said  attorneys-in-fact  and
agents or any of them, or their substitutes, may lawfully do or cause to be done
by virtue hereof.
         This Power of  Attorney shall  remain in full  force  and  effect until
revoked by me in writing.
 IN WITNESS WHEREOF, I hereto set my hand this 15th day of May, 2001.

                                       /s/ Debra L. Reed
                                       -----------------------------------
                                           Debra L. Reed