1

                            VALERO ENERGY CORPORATION
                             SECRETARY'S CERTIFICATE


         The undersigned, Jay D. Browning, Secretary of VALERO ENERGY
CORPORATION, a Delaware corporation, (the "Company"), does hereby certify that
(i) at a meeting of the Board of Directors of the Company (the "Board") held on
May 4, 2001, the Board adopted resolutions that, among other things, approved an
Agreement and Plan of Merger (the "Merger"), by and between the Company and
Ultramar Diamond Shamrock Corporation, a Delaware corporation ("UDS"); (ii) the
above referenced resolutions included those attached hereto as EXHIBIT A, and
the resolutions set forth in EXHIBIT A are a true and correct copy of those
adopted by the Board on May 4, 2001 and have not been amended, altered,
modified, or revoked and remain in full force and effect on the date hereof.


         IN WITNESS WHEREOF, I have hereunto set my hand as of the 2ND day of
AUGUST, 2001.



                                             /s/ Jay D. Browning
                                             -----------------------------------
                                             Jay D. Browning
                                             Secretary





   2

                                    EXHIBIT A

                                                       APPROVED
                                                       BOARD OF DIRECTORS
                                                       VALERO ENERGY CORPORATION
                                                       MAY 4, 2001

Proxy Statement, Registration Statements
and Other Securities Law Filings

                  RESOLVED, further, that the proper officers of the Company be,
and each of them hereby is, authorized and directed for, on behalf of and in the
name of the Company, to prepare, sign and file, or cause to be filed, with the
Securities and Exchange Commission (the "Commission") any and all statements,
reports or other information concerning the Merger, the Agreement and the other
transactions contemplated thereby that may be deemed advisable or may be
required under the Exchange Act or the Securities Act of 1933, as amended (the
"Securities Act"), including without limitation a proxy statement (which may be
in the form of a joint proxy statement-prospectus) for delivery to the
shareholders of the Company (the "Proxy Statement") and a registration statement
on Form S-4 which shall include the Proxy Statement (the "S-4"), and any
amendment or amendments (including post-effective amendments or supplements)
thereto, relating to the shares of Company Common Stock as are issuable in the
merger, and registration statements on Form S-8 and any amendment or amendments
(including post-effective amendments or supplements) thereto, relating to shares
of Company Common Stock as may be issuable in connection with any UDS Benefit
Plans (as defined in the Agreement) assumed by the Company in the Merger
(together with the S-4, the "Registration Statements"), each together with any
other documents required or appropriate in connection therewith; and

Power of Attorney

                  RESOLVED, that each officer or Director who may be required to
sign the Registration Statements or any amendment, exhibit or other document
related thereto (whether for and on behalf of the Company, as an officer or
Director of the Company, or in any other capacity) be, and each hereby is,
authorized to execute a power of attorney appointing William E. Greehey, John D.
Gibbons and Jay D. Browning, and each of them, severally, as his or her attorney
and agent, with full power of substitution and resubstitution, on his or her
behalf in any such capacity to sign and file the Registration Statements and any
and all amendments, exhibits and other documents related thereto which any such
attorney or substitute may deem necessary or advisable to be filed with the
Commission, with full power and authority to perform and do any and all acts and
things whatsoever which any such attorney or substitute may deem necessary or
advisable to be performed or done in connection with any or all of the
above-described matters, as fully as such officer or Director might or could do
if personally present and acting and as fully as the Company might or could do
by a properly authorized agent.