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                                                                     EXHIBIT 5.1

                    [FULBRIGHT & JAWORSKI L.L.P. LETTERHEAD]



July 1, 1998



Tesoro Petroleum Corporation
8700 Tesoro Drive
San Antonio, Texas 78217

Gentlemen:

         We have acted as counsel to Tesoro Petroleum Corporation, a Delaware
corporation (the "Company"), in connection with (i) the preparation of a shelf
Registration Statement on Form S-3 (Registration No. 333-51789) filed by the
Company with the Securities and Exchange Commission (the "SEC") (such
Registration Statement, as amended, the "Registration Statement") for the
purpose of registering under the Securities Act of 1933, as amended, among other
securities, common stock of the Company (the "Common Stock") and depositary
shares; and (ii) the preparation of prospectus supplements in connection with
(x) the issuance of 5,000,000 shares of Common Stock (including 750,000 shares
of Common Stock subject to the underwriters' over-allotment option), and (y)
9,000,000 Premium Income Equity Securities ("PIES") (including 1,350,000 PIES
subject to the underwriters' over-allotment option) consisting of depositary
shares, each representing one one-hundredth of a share of Mandatorily
Convertible Preferred Stock (the "Prospectus Supplements"). Capitalized terms
used herein but not otherwise defined shall have the respective meanings set
forth in the Prospectus Supplements.

         In connection therewith, we have examined originals or copies certified
or otherwise identified to our satisfaction of the certificate of incorporation
of the Company, the by-laws of the Company, the corporate proceedings with
respect to the offering of shares of Common Stock and PIES and such other
documents and instruments as we have deemed necessary or appropriate for the
expression of the opinions contained herein.

         We have assumed the authenticity and completeness of all records,
certificates and other instruments submitted to us as originals, the conformity
to original documents of all records, certificates and other instruments
submitted to us as copies, the authenticity and completeness of the originals of
those records, certificates and




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Tesoro Petroleum Corporation
July 1, 1998
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other instruments submitted to us as copies and the correctness of all
statements of fact contained in all records, certificates and other instruments
that we have examined.

         Based on the foregoing, and having regard for such legal considerations
as we have deemed relevant, we are of the opinion that (i) the shares of Common
Stock, the PIES and the Mandatorily Convertible Preferred Stock represented by
such PIES, proposed to be issued have been duly and validly authorized for
issuance and, when issued, delivered, sold and paid for in accordance with the
terms of the Registration Statement and Prospectus Supplements, will be duly and
validly issued, fully paid and nonassessable, and (ii) that the shares of Common
Stock issuable upon conversion of the PIES have been duly authorized and
reserved for issuance upon conversion and, when issued upon such conversion in
accordance with the terms of the Certificate of Designation of the Mandatorily
Convertible Preferred Stock, will be validly issued, fully paid and
nonassessable.

         The opinions expressed herein relate solely to, are based solely upon 
and are limited exclusively to the laws of the States of New York and Texas, the
General Corporation Law of the State of Delaware and the federal laws of the
United States of America.

         We hereby consent to the use of our name under the caption "Legal 
Matters" in the Prospectus dated May 14, 1998, and in the supplements which form
a part of the Registration Statement. In giving this consent, we do not thereby
admit that we come within the category of persons whose consent is required
under Section 7 of the Securities Act of 1933, as amended, or the rules and
regulations of the Securities and Exchange Commission promulgated thereunder.


                                              Very truly yours,

                                              /s/ FULBRIGHT & JAWORSKI L.L.P.