EXHIBIT 5.1

                    [VALERO ENERGY CORPORATION LETTERHEAD]

                                January 31, 2002

Valero Energy Corporation
One Valero Place
San Antonio, Texas  78212

Ladies and Gentlemen:

      I am Vice President and Corporate Secretary of Valero Energy Corporation,
a Delaware corporation (the "Company"), and have acted as counsel for the
Company in connection with the preparation and filing with the Securities and
Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended (the "Securities Act") of a Registration Statement on Form S-4 (the
"Registration Statement") relating to registration under the Securities Act of
shares of Common Stock, par value $0.01 per share, of the Company (the "Common
Stock") issuable in connection with the merger of Ultramar Diamond Shamrock
Corporation ("UDS") with and into the Company, as contemplated by the Agreement
and Plan of Merger, dated as of May 6, 2001, by and between UDS and the Company
(the "Merger Agreement"), including the filing of a Post-Effective Amendment No.
1 on Form S-8 to the Registration Statement (the "Amendment").

      The Amendment relates to the registration of up to 7,940,000 shares of
Common Stock issuable pursuant to the Diamond Shamrock, Inc. 1987 Long Term
Incentive Plan, the Diamond Shamrock, Inc. Long-Term Incentive Plan, the Total
Petroleum (North America) Ltd. 1990 Stock Incentive Plan, the Ultramar
Corporation 1992 Long-Term Incentive Plan, the Ultramar Diamond Shamrock
Corporation Amended and Restated 1996 Long-Term Incentive Plan, the Ultramar
Diamond Shamrock Corporation Non-Employee Director Equity Plan, as amended
effective January 1, 2000, the Ultramar Diamond Shamrock Corporation 401(k)
Retirement Savings Plan, and the Ultramar Diamond Shamrock Corporation
Nonqualified 401(k) Plan (collectively, the "Plans"). Valero assumed the Plans
pursuant to the transactions contemplated by the Merger Agreement.

      In rendering this opinion, I have examined the Merger Agreement, the
Registration Statement, the Amendment, the Company's current Restated
Certificate of Incorporation and By-Laws and originals or copies, certified or
otherwise identified to my satisfaction, of such other documents, corporate
records, certificates of public officials and other instruments as I have deemed
necessary or advisable for the purpose of rendering this opinion. I have relied
as to certain matters on information obtained from public officials, officers of
the Company and other sources believed by me to be responsible.

      Based on the foregoing, I am of the opinion that the shares of Common
Stock, when sold and issued in accordance with the terms and conditions of the
Plans as described in the Amendment, will be validly issued, fully paid and
nonassessable.

      I am a member of the Bar of the State of Texas and my opinion is limited
to the federal statutory laws of the United States, the laws of the State of
Texas and the Delaware General Corporation Law.

      I hereby consent to the filing of this opinion as an exhibit to the
Amendment. In giving such opinion, I do not thereby admit that I am in the
category of persons whose consent is required under Section 7 of the Securities
Act.

                                    Very truly yours,

                                       /s/ Jay D. Browning
                                       -------------------
                                       Jay D. Browning
                                       Vice President and Corporate Secretary