[Apache Letterhead]

                                                                     EXHIBIT 5.1


                                  July 31, 2002


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

Gentlemen:

         I am rendering this opinion in my capacity as Attorney for Apache
Corporation, a Delaware corporation ("Apache"), in connection with the
Registration Statement on Form S-8 (the "Registration Statement") filed on or
about this date by Apache under the Securities Act of 1933, as amended, and
relating to 200,000 shares of Apache's common stock, $1.25 par value ("Apache
Common Stock"), to be offered under the plan described in the Registration
Statement (the "Plan").

         In connection therewith, I have examined the Registration Statement,
the corporate proceedings with respect to the offering of shares and such other
documents and instruments as I have deemed necessary or appropriate for the
expression of the opinion contained herein.

         On the basis of the foregoing, and having regard for such legal
considerations I have deemed relevant, it is my opinion that the 200,000 shares
of Apache Common Stock to be registered have been duly authorized for issuance
and sale, and when issued in accordance with the terms and conditions of the
Plan, will be legally issued, fully paid and non-assessable.

     The opinions set forth above are limited in all respects to matters of
     Texas law and to the Delaware General Corporation Law (including the
     applicable provisions of the Delaware Constitution and the reported
     judicial decisions interpreting these laws).

         I consent to the inclusion of this letter as an exhibit to the
Registration Statement and to the reference in the Prospectus included as part
of the Registration Statement to my having issued the opinion expressed herein.


                                           Very truly yours,



                                           /s/ Jeffrey B. King
                                           Jeffrey B. King
                                           Corporate Counsel