Unocal Corporation
                                               2141 Rosecrans Avenue, Suite 4000
                                               El Segundo, California 90245
                                               Telephone (310) 726-7651
                                               Facsimile (310) 726-7815



                           UNOCAL [Logo Appears Here]




                                                June 28, 2002

Dennis P.R. Codon
Senior Vice President, Chief Legal Officer and General Counsel



Unocal Corporation
2141 Rosecrans Avenue
Suite 4000
El Segundo, California  90245

         Re:      2000 Executive Stock Purchase Plan
                  Registration Statement on Form S-3
                  -----------------------------------

Ladies and Gentlemen:

     I am the Senior Vice President, Chief Legal Officer and General Counsel of
Unocal Corporation, a Delaware corporation ("Unocal"), and as such I, and
attorneys working for me, have acted on behalf of Unocal as counsel in
connection with the preparation of the Registration Statement on Form S-3
(Registration No. 333-85864), as amended by Pre-Effective Amendment No. 1 (the
"Registration Statement"), which Unocal has filed with the Securities and
Exchange Commission. The Registration Statement relates to the registration
under the Securities Act of 1933, as amended (the "Securities Act"), of the
resale of 971,374 shares (the "Shares") of Unocal Common Stock, par value $1.00
per share, issued under the 2000 Executive Stock Purchase Plan (the "Plan").

     This opinion is rendered in accordance with the requirements of Item
601(b)(5) of Regulation S-K of the Securities and Exchange Commission.

     I, or such attorneys working for me, have examined or considered such
matters of law and fact and such corporate records, certificates and other
documents as I, or they, have deemed necessary, including, but not limited to:
the Restated Certificate of Incorporation and Bylaws of Unocal, as amended to
date; the Rights Agreement, dated as of January 5, 2000, between Unocal and
Mellon Investor Services, L.L.C., as Rights Agent, as amended by Amendment to
Rights Agreement, dated as of March 27, 2002; certain resolutions adopted by the
Board of Directors of Unocal at a meeting duly called and held on March 28,
2000; the Plan; and certificates and other information obtained from public
officials and officers and employees of Unocal and its subsidiaries. In the
course of such examination, I, and such attorneys working for me, have assumed
the genuineness of all signatures, the authenticity of all documents submitted
as originals and the conformity to the originals of all documents submitted as
certified, photostatic or conformed copies. I have relied, as to certain legal
matters, on the advice of such attorneys working for me who are more familiar
with such matters.

     I am licensed to practice law in the state of California and am familiar
with the Delaware General Corporation Law, the Delaware Constitution and
reported judicial decisions interpreting these laws. Therefore, the following
opinions are limited to the laws of the state of California, the Delaware
General Corporation Law and the Delaware Constitution and reported judicial
decisions interpreting these laws, and the federal laws of the United States, to
the exclusion of all other jurisdictions.

     Based on and subject to the foregoing, I am of the opinion that the Shares
were duly authorized for issuance by the Board of Directors of Unocal and that,
when one or more certificates evidencing the Shares has been duly countersigned
by the transfer agent and registrar for the Common Stock, and the Shares have
been issued to and paid for in accordance with the Plan and procedures
established between the transfer agent and registrar for the Common Stock and
The Depository Trust Company, the shares will be validly issued, fully paid and
non-assessable.

     I hereby consent to the filing of this opinion with the Securities and
Exchange Commission as an Exhibit to the Registration Statement and to the
reference to me under the caption "Legal Matters" therein. In giving this
consent, I do not thereby admit that I am included in the category of persons
whose consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission promulgated thereunder.

                                         Sincerely,


                                         /S/ Dennis P.R. Codon