EXHIBIT 5.1

                               UNOCAL CORPORATION
                              2141 Rosecrans Avenue
                                   Suite 4000
                           El Segundo California 90245
                            Telephone (310) 726-7763
                            Facsimile (310) 726-7877

                                [UNOCAL 76 LOGO]


Charles O. Strathman
Vice President and Chief Legal Officer



                                February 11, 2003


Union Oil Company of California
Unocal Corporation
Unocal Capital Trust II
2141 Rosecrans Avenue, Suite 4000
El Segundo, California 90245

RE: Registration Statement on Form S-3
    ----------------------------------

Ladies and Gentlemen:

         As Vice President and Chief Legal Officer of Union Oil Company of
California, a California corporation (the "Company"), and Unocal Corporation, a
Delaware corporation ("Unocal"), and as counsel for Unocal Capital Trust II, a
Delaware statutory trust (the "Trust"), I have examined, or caused to be
examined by attorneys working under my direction, the Registration Statement on
Form S-3 (the "Registration Statement"), including the exhibits thereto, which
the Company, Unocal and the Trust propose to file with the Securities and
Exchange Commission (the "Commission") concurrently with the delivery of this
letter.

         The Registration Statement relates to the registration under the
Securities Act of 1933, as amended (the "Securities Act"), for offering and sale
from time to time on a continuous or delayed basis pursuant to Rule 415 under
the Securities Act, of up to $1,200,000,000 aggregate public offering price (or
$1,538,800,000, pursuant to Rule 429 under the Securities Act, including
$338,800,000 aggregate offering price of Securities (as defined below)
registered and remaining unissued under the registration statement on form S-3
filed by the Company, Unocal and the Trust with the Commission on July 2, 1998
(Registration Nos. 333-58415, 333-58415-01 and 333-58415-02)), without
allocation as to class of securities, of (i) debt securities of the Company,
consisting of unsecured notes, debentures or other evidences of indebtedness,
which may be either senior (the "Company Senior Debt Securities") or
subordinated (the "Company Subordinated Debt Securities") and issuable in one or
more series, in each case, together with guarantees of Unocal as to the payment
of principal, interest and premium, if any, thereof (the "Unocal Debt Securities
Guarantees" and, together with the Company Senior Debt Securities and the




Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 2

Company Subordinated Debt Securities, the "Company Debt Securities"); (ii)
warrants of the Company and Unocal to purchase Company Debt Securities (the
"Debt Warrants"), which may be issued independently or together with any series
of Company Debt Securities; (iii) shares of Preferred Stock, par value $0.10 per
share, of Unocal (the "Unocal Preferred Stock"), issuable in one or more series;
(iv) shares of Common Stock, par value $1.00 per share, of Unocal (the "Unocal
Common Stock"), together with associated Preferred Share Purchase Rights of
Unocal (the "Rights"); (v) warrants of Unocal to purchase Unocal Preferred Stock
and Unocal Common Stock (the "Equity Warrants"), which may be issued
independently or together with shares of Unocal Preferred Stock or Unocal Common
Stock; (vi) Trust Preferred Securities (the "Trust Preferred Securities") of the
Trust, together with the guarantee thereof of Unocal to the extent set forth in
such guarantee (the "Preferred Securities Guarantee"); (vii) Junior Subordinated
Debentures of Unocal (the "Unocal Subordinated Debentures"), as to which the
Trust Preferred Securities would represent indirect undivided beneficial
interests; (viii) stock purchase contracts of Unocal (the "Unocal Stock Purchase
Contracts"), requiring or entitling the holder thereof to purchase from Unocal,
or Unocal to sell to such holder, Unocal Common Stock or Unocal Preferred Stock;
and (ix) stock purchase units of Unocal (the "Unocal Stock Purchase Units")
consisting of (1) a Unocal Stock Purchase Contract and (2) a beneficial interest
in Company Debt Securities, Trust Preferred Securities and/or debt obligations
of third parties. The shares of Unocal Preferred Stock and Unocal Common Stock
may be issued either directly, upon the conversion or exchange of Company Debt
Securities, pursuant to Unocal Stock Purchase Contracts, upon the exercise of
Equity Warrants or, in the case of shares of Unocal Common Stock, upon the
conversion of shares of Unocal Preferred Stock or the Trust Preferred Securities
and underlying Unocal Subordinated Debentures. The Rights will be issued only
with, and initially represented by the certificates for and transferable only
with, shares of Unocal Common Stock. All of the foregoing securities are
hereinafter referred to collectively as the "Securities."

         The Securities will be offered and sold in the manner described in the
Registration Statement, in the applicable prospectus contained therein (each a
"Prospectus" and, together, the "Prospectuses") and in supplements to a
Prospectus describing in detail the particular issue or series of Securities
offered thereby (each a "Prospectus Supplement"), each as filed with the
Commission. The Company Senior Debt Securities and related Unocal Debt
Securities Guarantees will be issued under the Indenture, dated as of February
3, 1995 (the "Company Senior Debt Indenture"), among the Company, Unocal and
Chemical Trust Company of California (which was succeeded by merger, effective
as of November 15, 1997, by Chase Manhattan Bank and Trust Company, National
Association, which was in turn succeeded by merger, effective as of December 1,
2001, by J.P. Morgan Trust Company, National Association), as Trustee, and the
Company Subordinated Debt Securities and related Unocal Debt Securities
Guarantees will be issued under an indenture (the "Company Subordinated Debt
Indenture" and, together with the Company Senior Debt Indenture, the "Company
Debt Indentures") to be entered into among the Company, Unocal and a Trustee to
be determined in the future.

         The Company Debt Indentures will incorporate by reference the Standard
Multiple-Series Indenture Provisions, January 1991, of the Company and Unocal,
dated as of January 2, 1991



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 3

(the "Standard Company Debt Indenture Provisions"). The Debt Warrants and Equity
Warrants will be issued pursuant to warrant agreements (each a "Warrant
Agreement") to be entered into among the Company and/or Unocal and one or more
Warrant Agents to be determined in the future. The Trust Preferred Securities
will be issued pursuant to an Amended and Restated Declaration of Trust of the
Trust (the "Trust Agreement"), to be entered into among Unocal, as Sponsor of
the Trust, Darrell D. Chessum, Daniel A. Franchi and Richard L. Walton, as the
Regular Trustees, The Bank of New York, as the Institutional Trustee, and The
Bank of New York (Delaware), as the Delaware Trustee. The Preferred Securities
Guarantee will be issued pursuant to a Preferred Securities Guarantee Agreement
to be entered into between Unocal and The Bank of New York, as the Guarantee
Trustee. The Unocal Subordinated Debentures will be issued pursuant to the
Multiple Series Indenture, dated as of September 11, 1996 (the "Base
Indenture"), between Unocal and The Bank of New York, as Trustee, and a Second
Supplemental Indenture (the "Supplemental Indenture" and, together with the Base
Indenture, the "Unocal Subordinated Debt Indenture") to be entered into between
Unocal and The Bank of New York, as Trustee. The Rights will be issued pursuant
to the Rights Agreement, dated as of January 5, 2000, as amended as of March 27
and August 2, 2002 (the "Rights Agreement"), between Unocal and Mellon Investor
Services, LLC, as Rights Agent. Forms of the Company Debt Indentures, the
Standard Company Debt Indenture Provisions, the Company Debt Securities, the
Warrant Agreements (including annexed forms of warrant certificates) the Trust
Agreement (including an annexed form of the Trust Preferred Securities), the
Preferred Securities Guarantee Agreement, the Base Indenture, the Supplemental
Indenture (including an annexed form of the Unocal Subordinated Debentures) and
the Rights Agreement (including amendments) are included as exhibits to the
Registration Statement.

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

         I am familiar with the actions heretofore taken by the Boards of
Directors and officers of the Company and Unocal and the Regular Trustees of the
Trust in connection with the preparation and filing of the Registration
Statement, the authorization of the Company Debt Indentures, the Base Indenture,
the Rights Plan and certain related matters. I have examined, or caused to be
examined by such attorneys working under my direction, and have considered such
questions of law and fact and such instruments, documents and records as I or
they have deemed relevant and necessary for the basis of the opinions expressed
below.

         I have relied, as to certain matters of fact, on information obtained
from public officials, officers of the Company and Unocal, the Regular Trustees
of the Trust and other sources believed by me to be responsible; and I have
assumed that the signatures (other than signatures executing documents on behalf
of the Company and Unocal and other than signatures of the Regular Trustees of
the Trust) on all documents examined or caused to be examined by me are genuine,
that all documents submitted to me as originals are authentic, and that all
documents submitted to me as copies conform with the originals, which
assumptions I have not independently verified. Also, I have relied, as to
certain legal matters, on advice of such attorneys work-



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 4

ing under my direction who are more familiar with such matters, as described in
the preceding paragraph.

         The opinions expressed below are limited to the laws of the State of
California, the Delaware General Corporation Law and the Federal laws of the
United States, all as currently in effect, to the exclusion of all other
jurisdictions and all other laws of the State of Delaware.

         The opinions expressed below are subject to the conditions that the
Registration Statement shall have become effective under the Securities Act,
that the applicable Indenture shall have been qualified under the Trust
Indenture Act of 1939, as amended, and that all applicable provisions of the
"Blue Sky" and securities laws of the various states and other jurisdictions in
which the Securities may be offered and sold shall have been complied with.

         The opinions expressed in Paragraphs 1, 2, 3, 6, 10, 11 and 13 below,
relating to whether the Securities described therein will be validly issued and
binding obligations of the Company and/or Unocal, are subject to the exception
that enforcement thereof may be limited by (i) bankruptcy, insolvency,
reorganization, moratorium and other laws relating to or affecting creditors'
rights generally, (ii) general principles of equity, regardless of whether
enforcement is sought in a proceeding in equity or at law, (iii) requirements
that a claim with respect to any Securities denominated other than in United
States dollars (or a judgment denominated other than in United States dollars in
respect of such a claim) be converted into United States dollars at a rate of
exchange prevailing on a date determined pursuant to applicable law, and (iv)
governmental authority to limit, delay or prohibit the making of payments
outside the United States or in a foreign currency, composite currency or
currency unit. In addition, I express no opinion with respect to the validity
and binding nature of the obligations of the Company and Unocal with respect to
any Securities that may be indexed or linked to any foreign currency, composite
currency, currency unit, commodity price, financial or non-financial index or
other factors.

         Based upon and subject to the foregoing, I am of the opinion that:

          1. When the applicable Company Debt Indenture under which any Company
Debt Securities of any series are to be issued has been duly executed and
delivered by the parties thereto, all requisite corporate action has been taken
by the Company and Unocal to establish the terms of and to authorize the
issuance of such Company Debt Securities under the applicable Company Debt
Indenture and the consideration to be received therefor, and such Company Debt
Securities have been duly completed and duly executed, authenticated, issued and
delivered, against payment therefor of the consideration specified by such
corporate action, in accordance with the applicable Company Debt Indenture and
in the manner described in such corporate action and in the Registration
Statement, the applicable Prospectus and the applicable Prospectus Supplement,
such Company Debt Securities will be validly issued and binding obligations of
the Company and Unocal.



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 5

          2. When all requisite corporate action has been taken by the Company
and Unocal to establish the terms of and to authorize the issuance of any series
of Debt Warrants and to authorize a Warrant Agreement relating thereto, the
applicable Company Debt Indenture under which Company Debt Securities of any
series are to be issued upon the exercise of such Debt Warrants has been duly
executed and delivered by the parties thereto, all requisite corporate action
has been taken to establish the terms of and to authorize the issuance of such
Company Debt Securities under the applicable Company Debt Indenture upon the
exercise of such Debt Warrants and the consideration to be received therefor
upon such exercise, the applicable Warrant Agreement has been duly executed and
delivered by the parties thereto and certificates evidencing such Debt Warrants
have been duly completed and duly executed, countersigned, issued and delivered,
against payment therefor of the consideration specified by such corporate
action, in accordance with the applicable Warrant Agreement and in the manner
described in such corporate action and in the Registration Statement, the
applicable Prospectus and the applicable Prospectus Supplement, such Debt
Warrants will be validly issued and binding obligations of the Company and
Unocal.

          3. When the applicable Company Debt Indenture under which Company Debt
Securities of any series are to be issued upon the exercise of any series of
Debt Warrants has been duly executed and delivered by the parties thereto, all
requisite corporate action has been taken by the Company and Unocal to establish
the terms of and to authorize the issuance of such Company Debt Securities under
the applicable Company Debt Indenture upon the exercise of such Debt Warrants
and the consideration to be received therefor upon such exercise, such Debt
Warrants have been duly and validly issued in the manner contemplated by
Paragraph 2 above and exercised in accordance with their terms and the terms of
the applicable Warrant Agreement and in the manner described in the Registration
Statement, the applicable Prospectus and the applicable Prospectus Supplement,
and such Company Debt Securities have been duly completed and duly executed,
authenticated, issued and delivered, against payment therefor of the
consideration specified by such corporate action, upon such exercise in
accordance with the applicable Company Debt Indenture and the applicable Warrant
Agreement and in the manner described in such corporate action and in the
Registration Statement, the applicable Prospectus and the applicable Prospectus
Supplement, such Company Debt Securities will be validly issued and binding
obligations of the Company and Unocal.

          4. When all requisite corporate action, including the adoption of
appropriate resolutions by the Board of Directors and/or a duly authorized
committee thereof (the "Board Resolutions"), has been taken by Unocal to
establish the terms of and to authorize the issuance of any shares of any series
of Unocal Preferred Stock, the consideration to be received therefor and a form
of certificate evidencing such shares of such series, a certificate setting
forth the voting powers, designations, preferences and relative, participating,
optional or other special rights, and qualifications, limitations or
restrictions (the "Certificate of Designations") of such series has been duly
executed and filed with the Secretary of State of the State of Delaware, and
certificates evidencing such shares have been duly executed, countersigned,
issued and delivered, against payment therefor of the consideration specified in
such Board Resolutions, in the manner



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 6

described in such Board Resolutions and in the Registration Statement, the
applicable Prospectus and the applicable Prospectus Supplement, such shares of
such series of Unocal Preferred Stock will be validly issued, fully paid and
nonassessable.

          5. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to authorize the
issuance of any shares of Unocal Common Stock and the consideration to be
received therefor, and certificates evidencing such shares have been duly
executed, countersigned, issued and delivered, against payment therefor of the
consideration specified in such Board Resolutions, in the manner described in
such Board Resolutions and in the Registration Statement, the applicable
Prospectus and the applicable Prospectus Supplement, such shares of Unocal
Common Stock will be validly issued, fully paid and nonassessable.

          6. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to establish the terms
of and to authorize the issuance of any series of Equity Warrants and to
authorize a Warrant Agreement relating thereto, to establish the terms of and to
authorize the issuance of shares of any series of Unocal Preferred Stock or to
authorize the issuance of any shares of Unocal Common Stock, as the case may be,
upon the exercise of such Equity Warrants and the consideration to be received
therefor upon such exercise, and to authorize a form of certificate evidencing
such shares of any such series of Unocal Preferred Stock, the Certificate of
Designations of any such series of Unocal Preferred Stock has been duly executed
and filed with the Secretary of State of the State of Delaware, the applicable
Warrant Agreement has been duly executed and delivered by the parties thereto
and certificates evidencing such Equity Warrants have been duly completed and
duly executed, countersigned, issued and delivered, against payment therefor of
the consideration specified in such Board Resolutions, in accordance with the
applicable Warrant Agreement and in the manner described in such Board
Resolutions and in the Registration Statement, the applicable Prospectus and the
applicable Prospectus Supplement, such Equity Warrants will be validly issued
and binding obligations of Unocal.

          7. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to establish the terms
of and to authorize the issuance of any shares of any series of Unocal Preferred
Stock or to authorize the issuance of any shares of Unocal Common Stock, as the
case may be, upon the conversion or exchange of Company Debt Securities of any
series providing for such conversion or exchange and the consideration to be
received therefor upon such conversion or exchange, and to authorize a form of
certificate evidencing any such shares of any such series of Unocal Preferred
Stock, the Certificate of Designations of any such series of Unocal Preferred
Stock has been duly executed and filed with the Secretary of State of the State
of Delaware, such Company Debt Securities have been duly and validly issued in
the manner contemplated by Paragraph 1 or 3 above and surrendered to Unocal or
its duly authorized agent for conversion or exchange, as the case may be, in
accordance with their terms and the terms of the applicable Company Debt
Indenture, and certificates evidencing such shares of such series of Unocal
Preferred Stock or such shares of Unocal Common Stock, as



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 7

the case may be, have been duly executed, countersigned, issued and delivered,
against receipt by Unocal of the consideration specified in such Board
Resolutions, upon such conversion or exchange in accordance with the terms of
such Company Debt Securities and the terms of the applicable Company Debt
Indenture, such shares of such series of Unocal Preferred Stock or such shares
of Unocal Common Stock, as the case may be, will be validly issued, fully paid
and nonassessable.

          8. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to establish the terms
of and to authorize the issuance of any shares of any series of Unocal Preferred
Stock or to authorize the issuance of any shares of Unocal Common Stock, as the
case may be, upon the exercise of any series of Equity Warrants and the
consideration to be received therefor upon such exercise, and to authorize a
form of certificate evidencing any such shares of any such series of Unocal
Preferred Stock, the Certificate of Designations of any such series of Unocal
Preferred Stock has been duly executed and filed with the Secretary of State of
the State of Delaware, such Equity Warrants have been duly and validly issued in
the manner contemplated by Paragraph 6 above and exercised in accordance with
their terms and the terms of the applicable Warrant Agreement and in the manner
described in the Registration Statement, the applicable Prospectus and the
applicable Prospectus Supplement, and certificates evidencing such shares of
such series of Unocal Preferred Stock or such shares of Unocal Common Stock, as
the case may be, have been duly executed, countersigned, issued and delivered,
against payment therefor of the consideration specified in such Board
Resolutions, upon such exercise in accordance with the applicable Warrant
Agreement and in the manner described in such Board Resolutions and in the
Registration Statement, the applicable Prospectus and the applicable Prospectus
Supplement, such shares of such series of Unocal Preferred Stock or such shares
of Unocal Common Stock, as the case may be, will be validly issued, fully paid
and nonassessable.

          9. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to authorize the
issuance of any shares of Unocal Common Stock upon the conversion of any shares
of any series of Unocal Preferred Stock providing for such conversion and the
consideration to be received therefor upon such conversion, such shares of such
series of Unocal Preferred Stock have been duly and validly issued in the manner
contemplated by Paragraph 4, 7 or 8 above and surrendered to Unocal or its duly
authorized agent for conversion in accordance with their terms and the terms of
the Certificate of Designations of such series, and certificates evidencing such
shares of Unocal Common Stock have been duly executed, countersigned, issued and
delivered, against receipt by Unocal of the consideration specified in such
Board Resolutions, upon such conversion in accordance with the Certificate of
Designations of such series of Unocal Preferred Stock, such shares of Unocal
Common Stock will be validly issued, fully paid and nonassessable.

          10. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to authorize the
Supplemental Indenture, under which Unocal Subordinated Debentures are to be
issued, and such Supplemental Indenture has



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 8

been duly executed and delivered by the parties thereto, all requisite corporate
action, including the adoption of appropriate Board Resolutions, has been taken
by Unocal to establish the terms of and to authorize the issuance to the Trust
of such Unocal Subordinated Debentures under such Unocal Subordinated Debt
Indenture and the consideration to be received therefor, and such Unocal
Subordinated Debenture have been duly completed and duly executed,
authenticated, issued and delivered to the Trust against payment therefor of the
consideration specified by such corporate action, in accordance with the Unocal
Subordinated Debt Indenture and in the manner described in such corporate action
and in the Registration Statement, the applicable Prospectus and the applicable
Prospectus Supplement, such Unocal Subordinated Debentures will be validly
issued and binding obligations of Unocal.

          11. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to authorize the
Preferred Securities Guarantee Agreement, under which the Preferred Securities
Guarantee is to be issued, and such Preferred Securities Guarantee Agreement has
been duly executed and delivered by the parties thereto concurrently with the
issuance and sale of the Trust Preferred Securities by the Trust, against
payment therefor of the consideration specified by such corporate action, in
accordance with the Trust Agreement and in the manner described in such
corporate action and in the Registration Statement, the applicable Prospectus
and the applicable Prospectus Supplement, such Preferred Securities Guarantee
will be a valid and binding obligation of Unocal.

          12. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to authorize the
issuance of shares of Unocal Common Stock upon the conversion or exchange of
Unocal Subordinated Debentures and related Trust Preferred Securities providing
for such conversion or exchange and the consideration to be received therefor
upon such conversion or exchange, such Unocal Subordinated Debentures have been
duly and validly issued in the manner contemplated by Paragraph 10 above and
surrendered to Unocal or its duly authorized agent for conversion or exchange,
as the case may be, in accordance with their terms and the terms of the Unocal
Subordinated Debt Indenture, and certificates evidencing such shares of Unocal
Common Stock have been duly executed, countersigned, issued and delivered,
against receipt by Unocal of the consideration specified in such Board
Resolutions, upon such conversion or exchange in accordance with the terms of
such Unocal Subordinated Debentures and the terms of the Unocal Subordinated
Debt Indenture, such shares of Unocal Common Stock will be validly issued, fully
paid and nonassessable.

          13. When all requisite corporate action, including the adoption of
appropriate Board Resolutions, has been taken by Unocal to establish the terms
of and to authorize the issuance of Unocal Stock Purchase Contracts, and to
authorize the applicable Unocal Stock Purchase Contract or other agreement
pursuant to which the Unocal Stock Purchase Contract is issued and the
consideration to be received therefor, and such Unocal Stock Purchase Contract
or other agreement has been duly executed and delivered by the parties thereto
against payment therefor of the consideration specified in such Board
Resolutions, in accordance with such Unocal Stock Purchase Contract or other
agreement and in the manner described in such Board Resolutions



Unocal Oil Company of California
Unocal Corporation
Unocal Capital Trust II
February 11, 2003
Page 9

and in the Registration Statement, the applicable Prospectus and the applicable
Prospectus Supplement, such Unocal Stock Purchase Contracts will be validly
issued and binding obligations of Unocal.

          14. The Rights have been duly authorized and, when such Rights are
issued in accordance with the Rights Agreement, together with shares of Unocal
Common Stock duly and validly issued in the manner contemplated by Paragraphs 5,
7, 8, 9 and/or 12 above, such Rights will be validly issued.

          I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the references to me under the caption "Validity
of the Securities" in each of the Prospectuses forming a part of the
Registration Statement. 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.


                                   Very truly yours,



                                   /s/ CHARLES O. STRATHMAN