EXHIBIT 5.2

                                 February 11, 2003


Unocal Capital Trust II
c/o Unocal Corporation
2141 Rosecrans Avenue, Suite 4000
El Segundo, California  90245

         Re:      Unocal Capital Trust II

Ladies and Gentlemen:

            We have acted as special Delaware counsel to Unocal Capital Trust
II, a Delaware statutory trust (the "Trust"), in connection with certain matters
relating to the organization of the Trust and the proposed issuance of Preferred
Securities to beneficial owners pursuant to and as described in the Registration
Statement (and the Prospectus forming a part thereof) on Form S-3 to be filed
with the Securities and Exchange Commission on or about the date hereof (the
"Registration Statement"). Capitalized terms used herein and not otherwise
herein defined are used as defined in the form of Amended and Restated
Declaration of Trust of the Trust to be attached as an exhibit to the
Registration Statement (the "Governing Instrument").

            In rendering this opinion, we have examined copies of the following
documents in the forms provided to us: the Certificate of Trust of the Trust as
filed in the Office of the Secretary of State of the State of Delaware (the
"State Office") on June 30, 1998 (the "Certificate"); a Declaration of Trust of
the Trust dated as of June 30, 1998 (the "Original Governing Instrument"); the
Governing Instrument; the Multiple Series Indenture of Unocal Corporation dated
as of September 11, 1996 (the "Base Indenture"); the form of Preferred
Securities Guarantee Agreement to be entered into between Unocal Corporation and
The Bank of New York, as trustee (the "Preferred Guarantee"); the form of Second
Supplemental Indenture, supplementing the Base Indenture, to be entered into
between Unocal Corporation and The Bank of New York, as trustee; the form of
Underwriting Agreement relating to the Preferred Securities (the "Underwriting
Agreement"); the Registration Statement; and a certification of good standing of
the Trust obtained as of a recent date from the State Office. In such
examinations, we have

Unocal Capital Trust II
February 11, 2003
Page 2

assumed the genuineness of all signatures, the conformity to original documents
of all documents submitted to us as drafts or copies or forms of documents to be
executed and the legal capacity of natural persons to complete the execution of
documents. We have further assumed for purposes of this opinion: (i) the due
formation or organization, valid existence and good standing of each entity
(other than the Trust) that is a party to any of the documents reviewed by us
under the laws of the jurisdiction of its respective formation or organization;
(ii) the due authorization, execution and delivery by, or on behalf of, each of
the parties thereto of the above-referenced documents; (iii) that no event has
occurred subsequent to the filing of the Certificate, or will occur prior to the
issuance by the Trust of Preferred Securities, that would cause a dissolution or
liquidation of the Trust under the Original Governing Instrument or the
Governing Instrument, as applicable; (iv) that the activities of the Trust have
been and will be conducted in accordance with the Original Governing Instrument
or the Governing Instrument, as applicable, and the Delaware Statutory Trust
Act, 12 Del. C. Section 3801 et seq. (the "Delaware Act"); (v) that Unocal
Corporation, as Sponsor, the Regular Trustees, the Institutional Trustee, the
Delaware Trustee and each other party thereto will duly authorize, execute and
deliver the Governing Instrument, the Underwriting Agreement and all other
documents contemplated thereby or by the Registration Statement to be executed
in connection with the issuance by the Trust of Preferred Securities, prior to
the first issuance of Preferred Securities; (vi) that the Preferred Securities
will be offered and sold pursuant to the Registration Statement and a prospectus
supplement that will be consistent with, and accurately describe, the terms of
the Governing Instrument and the Preferred Guarantee and all other relevant
documents; (vii) that prior to the first issuance of Preferred Securities,
payment of the required consideration therefor will have been made in accordance
with the terms and conditions of the Governing Instrument, the Registration
Statement, the prospectus supplement and the Underwriting Agreement and that the
Preferred Securities are otherwise issued and sold to the Preferred Securities
Holders in accordance with the terms, conditions, requirements and procedures
set forth in the Governing Instrument, the Registration Statement, the
prospectus supplement and the Underwriting Agreement; and (viii) that the
documents examined by us are in full force and effect, express the entire
understanding of the parties thereto with respect to the subject matter thereof
and have not been amended, supplemented or otherwise modified, except as herein
referenced. We have not reviewed any documents other than those identified above
in connection with this opinion, and we have assumed that there are no other
documents that are contrary to or inconsistent with the opinions expressed
herein. No opinion is expressed with respect to the requirements of, or
compliance with, federal or state securities or blue sky laws. We express no
opinion as to, and assume no responsibility for, the Registration Statement or
any other offering materials relating to the Preferred Securities. As to any
fact material to our opinion, other than those assumed, we have relied without
independent investigation on the above-referenced documents and on the accuracy,
as of the date hereof, of the matters therein contained.

Unocal Capital Trust II
February 11, 2003
Page 3

            Based on and subject to the foregoing, and limited in all respects
to matters of Delaware law, it is our opinion that:

            1.    The Trust is a duly formed and validly existing statutory
trust in good standing under the laws of the State of Delaware.

            2.    The Preferred Securities, upon issuance, will constitute
validly issued and, subject to the qualifications set forth in paragraph 3
below, fully paid and nonassessable beneficial interests in the assets of the
Trust.

            3.    Under the Delaware Act and the terms of the Governing
Instrument, each Preferred Security Holder of the Trust, in such capacity, will
be entitled to the same limitation of personal liability as that extended to
stockholders of private corporations for profit organized under the General
Corporation Law of the State of Delaware; provided, however, we express no
opinion with respect to the liability of any Preferred Security Holder who is,
was or may become a named Trustee of the Trust. Notwithstanding the foregoing,
we note that pursuant to Section 11.4 of the Governing Instrument, the Trust may
withhold amounts otherwise distributable to a Holder and pay over such amounts
to the applicable jurisdictions in accordance with federal, state and local law
and any amount withheld will be deemed to have been distributed to such Holder
and that, pursuant to the Governing Instrument, Preferred Security Holders may
be obligated to make payments or provide indemnity or security under the
circumstances set forth therein.

            We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of our name and reference to our opinion
under the heading "VALIDITY OF THE SECURITIES" in the Prospectus forming a part
thereof. 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 thereunder. This opinion speaks only as of the date hereof
and is based on our understandings and assumptions as to present facts, and on
our review of the above referenced documents and the application of Delaware law
as the same exist as of the date hereof, and we undertake no obligation to
update or supplement this opinion after the date hereof for the benefit of any
person or entity with respect to any facts or circumstances that may hereafter
come to our attention or any changes in facts or law that may hereafter occur or
take effect. This opinion is intended solely for the benefit of the addressee
hereof in connection with the matters contemplated hereby and may not be relied
on by any other person or entity or for any other purpose without our prior
written consent.

                                          Very truly yours,

                                          MORRIS, NICHOLS, ARSHT & TUNNELL

                                          /s/ Morris, Nichols, Arsht & Tunnell