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                                                                     EXHIBIT 5.1

                     [VALERO ENERGY CORPORATION LETTERHEAD]


                                        , 2001
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Valero Energy Corporation
One Valero Place
San Antonio, Texas  78212

Ladies and Gentlemen:

     I am the Corporate Secretary and Managing Attorney, Corporate Law 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").

     I have examined the Merger Agreement 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
have been duly authorized and (i) when the Registration Statement has become
effective under the Securities Act and (ii) when the shares of Common Stock have
been duly executed, countersigned and delivered by the Company upon the
consummation of the transaction as contemplated in the Merger Agreement and the
Registration Statement, such shares of Common Stock 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
Registration Statement and to the reference to me under the heading "Legal
Matters" in the proxy statement / prospectus that forms a part of the
Registration Statement. In giving such


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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,



                           -----------------------------
                           Jay D. Browning
                           Corporate Secretary and
                           Managing Attorney, Corporate Law