Exhibit 5.1

                     [UNION PACIFIC RESOURCES LETTERHEAD]

                                                                August 25, 1998

Union Pacific Resources Group Inc.
801 Cherry Street
Fort Worth, Texas 76102


         RE:      Union Pacific Resources Group Inc.

                  UPRG Capital Trust I

                  UPRG Capital Trust II

                  UPRG Capital Trust III

                  Union Pacific Resources Inc.

                  UPR Capital Company

                  Registration Statement on Form S-3

Dear Sirs:

         I am the Managing Senior Counsel of Union Pacific Resources Group
Inc., a Utah corporation (the "Company"), and am rendering this opinion in
connection with the Registration Statement on Form S-3 (the "Registration
Statement") of the Company, Union Pacific Resources Inc., an Alberta
corporation and indirect wholly owned subsidiary of the Company ("UPRI"), UPC
Capital Company, a Nova Scotia unlimited liability company and indirect wholly
owned subsidiary of the Company ("UPRCC" and together with UPRI, the
"Subsidiary Issuers") and UPRG Capital Trust I, UPRG Capital Trust II and UPRG
Capital Trust III, each a Delaware statutory business trust (collectively, the
"UPRG Trusts") being filed today with the Securities and Exchange Commission
under the Securities Act of 1933, as amended (the "Securities Act"), with
respect to (a) the following Securities of the Company: (i) unsecured senior
debt securities (the "Company Senior Debt Securities"), (ii) unsecured
subordinated debt securities (the "Company Subordinated Debt Securities" and,
together with the Company Senior Debt Securities, the "Company Debt
Securities"), (iii) warrants to purchase Company Senior Debt Securities (the
"Debt Warrants"), (iv) shares of preferred stock, without par value, of the
Company (the "Preferred Stock"), (v) warrants to purchase shares of Preferred
Stock (the "Preferred Stock Warrants"), (vi) shares of common stock, without
par value, of the Company (the "Common Stock"), (vii) warrants to purchase
shares of Common Stock (the "Common Stock Warrants"), (viii) stock purchase
contracts ("Stock Purchase Contracts") to purchase shares of Common Stock or
Preferred Stock, (ix) stock purchase units ("Stock Purchase Units"), each
representing ownership of a Stock Purchase Contract and Debt Securities (as
defined below), debt obligations of the United States of America or agencies
or instrumentalities thereof or Trust Preferred Securities (as defined below),
securing the holder's obligation to purchase shares of Common Stock or
Preferred Stock under the Stock Purchase Contract, in amounts, at prices and
on terms to be determined by market conditions at the time of offering; and
(x) guarantees of the Subsidiary Debt Securities (as defined below) (the
"Company Guarantees") and the Trust Preferred Securities; (b) the following
securities of the Subsidiary Issuers: (i) non-convertible unsecured senior
debt securities (the "Subsidiary Senior Debt Securities", together with the
Company Senior Debt Securities, the "Senior Debt Securities") and (ii)
non-convertible unsecured subordinated debt securities (the "Subsidiary
Subordinated Debt Securities" and, together with the Subsidiary Senior Debt
Securities, the "Subsidiary Debt Securities"; the Subsidiary Debt Securities,
together with the Company Debt Securities, the "Debt Securities") and (c) the
following securities of the UPRG Trusts: (i) preferred securities (the "Trust
Preferred Securities"), each of such securities listed under clauses (a), (b)
and (c) are for issuance from time to time pursuant to Rule 415 under the
Securities Act. The Debt Warrants, Preferred Stock Warrants and Common Stock
Warrants are referred to herein collectively as the "Warrants".

     I have examined (i) the form of the Indenture (the "Senior Indenture")
between the Company, the Subsidiary Issuers and The Bank of New York, as trustee
(the "Senior Trustee"), pursuant to which the Senior Debt Securities will be
issued, and (ii) I have examined such other documents and made such other
investigations as I have deemed necessary or advisable for purposes of this
opinion. Based thereon, I am of the opinion that:

         1. The Company is a corporation duly organized and validly existing
under the laws of the State of Utah.



         2.       Each of the Subsidiary Issuers is a corporation or unlimited
                  liability company, as applicable, duly formed and validly
                  existing under the laws of the jurisdiction of its
                  formation.

         3.       The execution and delivery of the Senior Indenture by the
                  Company and each Subsidiary Issuer and the issuance and sale
                  of Senior Debt Securities have been validly authorized by
                  all necessary corporate action by the Company and each
                  Subsidiary Issuer, as applicable.

         4.       When (i) the Registration Statement shall have become 
                  effective under the Securities Act, (ii) the blue sky or
                  securities laws of certain states shall have been complied
                  with, (iii) the Senior Indenture shall have been executed and
                  delivered by the Company, the Subsidiary Issuers and the
                  Senior Trustee and duly qualified under the Trust Indenture
                  Act of 1939, as amended, and (iv) the Senior Debt Securities
                  shall have been duly authorized, executed, authenticated and
                  delivered against payment therefor or upon exercise of
                  Warrants, and the Company shall have received any additional
                  consideration which is payable upon such exercise, the Senior
                  Debt Securities and the Company Guarantees shall each
                  constitute binding obligations of the Company and the
                  Subsidiary Issuers, as applicable, enforceable in accordance
                  with their terms, except as enforceability may be limited by
                  bankruptcy, insolvency, reorganization or other laws relating
                  to or affecting creditors' rights generally and subject to
                  general principles of equity.

         5.       When (i) the Registration Statement shall have become
                  effective under the Securities Act, (ii) the blue sky or
                  securities laws of certain states shall have been complied
                  with, and (iii) the Preferred Stock shall have been (A)
                  authorized, issued and sold as contemplated by the
                  Registration Statement and the Company shall have received
                  consideration therefor or (B) issued upon exercise of
                  Warrants, the Preferred Stock will be validly issued, fully
                  paid and non-assessable.

         6.       When (i) the Registration Statement shall have become
                  effective under the Securities Act, (ii) the blue sky or
                  securities laws of certain states shall have been complied
                  with, and (iii) the Common Stock shall have been (A)
                  authorized, issued and sold as contemplated by the
                  Registration Statement and the Company shall have received
                  consideration therefor or (B) issued upon exercise of
                  Warrants, the Common Stock will be validly issued, fully paid
                  and non-assessable.

         7.       When (i) the Registration Statement shall have become
                  effective under the Securities Act, (ii) the blue sky or
                  securities laws of certain states shall have been complied
                  with, (iii) a warrant agreement or agreements shall have been
                  authorized, executed and delivered by the Company and a
                  warrant agent, and (iv) the Warrants shall have been duly
                  executed and delivered against payment therefor, the Warrants
                  shall be legally issued.

         8.       When (i) the Registration Statement shall have become
                  effective under the Securities Act, (ii) the blue sky or
                  securities laws of certain states shall have been complied
                  with, (iii) a Stock Purchase Contract or Stock Purchase Unit
                  shall have been authorized and executed and delivered in
                  accordance with the Term 5 thereof and (iv) the Stock
                  Purchasers Contracts or Stock Purchase Units, as applicable,
                  shall have been delivered against payment therefor, the Stock
                  Purchase Contracts or Stock Purchase Units, as applicable,
                  shall be legally issued.

     This opinion is limited to laws of the State of New York, the corporate
laws of the States of Utah and Delaware, and applicable Federal laws of the
United States; provided that, as to matters of the law of the Provinces of
Alberta and Nova Scotia and federal laws of Canada, I have relied exclusively
upon opinions attached hereto.
         
     I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. I also consent to the use of my name under the caption
"Legal Opinions" in the Prospectus contained in the Registration Statement.

                                             Very truly yours,


                                             /s/ Mark L. Jones


                                             Mark L. Jones