<DOCUMENT>
<TYPE>EX-24.3_438969
<SEQUENCE>2
<FILENAME>poa.txt
<DESCRIPTION>POA DOCUMENT
<TEXT>
LIMITED POWER OF ATTORNEY
      The undersigned, Michael W. Conlon, hereby authorizes each of John E.
Vollmer III, Seth D. Wexler, and Barry Huntsman (with full power to each of them
to act alone), as the undersigned's true and lawful attorney-in-fact, with full
power of substitution to:
      (1) prepare and sign in the name of and on behalf of the undersigned any
and all forms and reports required to be filed pursuant to Section 16 of the
Securities Exchange Act of 1934 and the rules thereunder, including, but without
limitation, Form ID (Uniform Application For Access Codes to File on EDGAR),
Form 3 Initial Statement of Beneficial Ownership of Shares of Securities, Form 4
Statement of Changes of Beneficial Ownership of Securities, and Form 5 Annual
Statement of Beneficial Ownership of Securities;
      (2) perform any and all acts for and on behalf of the undersigned which
may be necessary or desirable to complete and execute any such Forms 3, 4 or 5,
or other form or report, and timely file such form or report with the United
States Securities and Exchange Commission and any stock exchange or similar
authority; and
      (3) take any other action of any type in connection with the foregoing
which, in the opinion of the attorney-in-fact, may be of benefit to, in the best
interest of, or legally required by, the undersigned, it being understood that
the documents executed by such attorney-in-fact on behalf of the undersigned
pursuant to this Limited Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney-in-fact may approve in such
attorney-in-fact's discretion.
      The undersigned hereby grants to each such attorney-in-fact full power to
do and perform any and every act requisite, necessary or proper to be done in
the exercise of any of the rights or powers herein granted, as fully to all
intents and purposes as the undersigned might or could do if personally present,
with full power of substitution or revocation, hereby ratifying and confirming
all that such attorney-in-fact, or such attorney-in-fact's substitute or
substitutes, shall lawfully do or cause to be done by virtue of this Limited
Power of Attorney and the rights and powers herein granted.  The undersigned
acknowledges that the foregoing attorney-in-fact, in serving in such capacity at
the request of the undersigned, is not assuming any of the undersigned's
responsibilities to comply with Section 16 of the Securities Exchange Act of
1934.
      This Limited Power of Attorney shall remain in effect until the
undersigned is no longer required to file Forms 3, 4 and 5 with respect to the
undersigned's beneficial ownership of securities, unless earlier revoked by the
undersigned in a signed and dated writing delivered to each of the foregoing
attorneys-in-fact.
      By execution of this Limited Power of Attorney, the undersigned revokes
all powers previously granted with respect to the preparation, execution and
filing of Section 16 forms and reports.
      EXECUTED THIS 20TH  DAY OF SEPTEMBER, 2012
/s/ Michael W. Conlon
Name:     Michael W. Conlon

THE STATE OF TEXAS

COUNTY OF HARRIS

       This instrument was acknowledged before me on September 20, 2012, by
Michael W. Conlon.

(SEAL)
/s/ Peggy Ann Rabalais
	Notary Public, State of Texas
 Peggy Ann Rabalais
	Printed Name of Notary   My commission expires: 11-12-15

</TEXT>
</DOCUMENT>
