1
                                                                     EXHIBIT 5.1

                        [APACHE CORPORATION LETTERHEAD]


                                November 11, 1999


Apache Corporation
2000 Post Oak Blvd., Suite 100
Houston, Texas 77056-4400

Lades and Gentlemen:

         I am General Counsel to Apache Corporation, a Delaware Corporation (the
"Company"), and am rendering this opinion in my capacity as such in connection
with the registration under the Securities Act of 1933, as amended, of
$400,000,000 aggregate principal amount of the senior unsecured debt securities
(the "Securities") of Apache Finance Canada Corporation, a Nova Scotia unlimited
liability company and an indirect wholly-owned subsidiary of the Company (the
"Issuer"), described in the registration statement on Form S-3 (the
"Registration Statement") of the Company and the Issuer. The Securities are to
be offered upon the terms and subject to the conditions set forth in one or more
underwriting agreements by and between the Company, the Issuer and the persons
to be named as underwriters therein ("Underwriting Agreement"). The Securities
are to be issued in one or more series pursuant to an Indenture among the
Company, the Issuer and The Chase Manhattan Bank, Trustee. The Securities are to
be irrevocably and unconditionally guaranteed (the "Guarantees") by the Company.

         In connection herewith, I have examined the Registration Statement
covering the Securities which is to be filed with the Securities and Exchange
Commission, originals or copies certified or otherwise identified to my
satisfaction of the charter documents of the Issuer, the restated certificate of
incorporation and the by-laws of the Company, each as amended to date, the
corporate proceedings with respect to the offering of the Securities and such
other documents and instruments as I have deemed necessary or appropriate for
the expression of the opinions contained herein.

         I have assumed the authenticity and completeness of all records,
certificates and other instruments presented to be originals, the conformity to
original documents of all records, certificates, and other instruments submitted
to me as copies, the authenticity and completeness of the originals of those
records, certificates and other instruments submitted to me as copies and the
correctness of all statements of fact contained in all records, certificates and
other instruments that I have examined.

   2
November 11, 1999
Page 2


         Based on the foregoing, and having regard for such legal considerations
as I have deemed relevant, I am of the opinion that: (a) the Securities, when
duly authorized and duly executed by the proper officers of the Issuer,
authenticated and delivered by the Trustee in accordance with the Indenture, and
issued and sold pursuant to the terms of the Underwriting Agreement against
payment of the consideration therefor, will constitute valid and legally binding
obligations of the Issuer, enforceable in accordance with their terms and (b)
the Guarantees, when duly authorized and duly executed by the proper officers of
the Company, the Securities to which such Guarantees relate have been
authenticated and delivered by the Trustee in accordance with the Indenture and
issued pursuant to the terms of the Underwriting Agreement against payment of
the consideration therefor, the Guarantees will constitute valid and legally
binding obligations of the Company, enforceable in accordance with their terms.

         The opinions expressed above regarding the enforceability of the
Securities and the Guarantees are subject to the exception that the enforcement
thereof may be limited by bankruptcy, insolvency, reorganization, moratorium or
other laws relating to or affecting enforcement of creditors' rights generally
or by general equity principles, and except further as enforcement thereof may
be limited by (i) requirements that claims with respect to any Securities
denominated other than in U.S. Dollars (or a foreign currency or composite
currency in respect of such claim) be converted into U.S. Dollars at a rate of
exchange prevailing on a date determined pursuant to applicable law or (ii)
governmental authority to limit, delay or prohibit the making of payments
outside the United States.

         With your consent, I have relied solely on the opinion of McInnes,
Cooper & Robertson, filed as Exhibit 5.2 to the Registration Statement, as to
matters governed by the laws of Canada and the Province of Nova Scotia.

         I consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of my name under the caption "Legal
Matters" in the Prospectus included as part of the Registration Statement. In
giving such consent, I do not admit that I am in the category of persons whose
consent is required under Section 7 of the Securities Act of 1933, as amended.

                                            Very truly yours,