EXHIBIT 8.1

                        [Mayer, Brown & Platt Letterhead]

                                October 30, 2001

Devon Energy Corporation
20 North Broadway, Suite 1500
Oklahoma City, Oklahoma 73102

Devon Holdco Corporation
20 North Broadway, Suite 1500
Oklahoma City, Oklahoma 73102

Ladies and Gentlemen:

         In connection with the registration statement on Form S-4, as amended
(the "Registration Statement"), filed by Devon Energy Corporation ("Devon") and
Devon Holdco Corporation, a wholly owned subsidiary of Devon ("Devon Holdco"),
relating to the transactions contemplated by the Amended and Restated Merger
Agreement, dated as of August 13, 2001 (the "Merger Agreement"), by and among
Devon, Devon NewCo Corporation, Devon Holdco, Devon Merger Corporation, Mitchell
Merger Corporation and Mitchell Energy & Development Corp., you have requested
our opinion regarding the description of material tax consequences related to
the Merger and the Alternate Mergers (in each case, as defined in the Merger
Agreement) as described in the Registration Statement.

         In formulating our opinion, we have examined the Merger Agreement and
the Registration Statement, including the joint proxy statement/prospectus that
forms a part of the Registration Statement. In addition, we have examined such
other documents, instruments and information as we considered necessary to
enable us to express this opinion. Our opinion is also based on (1) the accuracy
of the statements and facts concerning the Merger and the Alternate Mergers set
forth in the Merger Agreement (including, without limitation, the exhibits
thereto) and the Registration Statement, (2) the consummation of the Merger or
the Alternate Mergers, as the case may be, in the manner contemplated by, and in
accordance with the terms set forth in, the Merger Agreement and the
Registration Statement and (3) currently applicable provisions of the federal
income tax laws, including the Internal Revenue Code of 1986, as amended,
applicable Treasury Regulations promulgated thereunder, judicial authority and
current administrative rulings and practice.

         Based on the foregoing, as of the date hereof, we adopt and confirm the
statements under the caption "Certain Federal Income Tax Considerations" in the
Registration Statement as our opinion of the material tax consequences of the
Merger and the Alternate Mergers, to the extent that such statements constitute
legal conclusions. We know that we are referred to in the Registration Statement
and we hereby consent to the use of our name therein and to the filing of this
opinion as part of the Registration Statement, without admitting that we are
"experts" within the meaning of the Securities and Exchange Act of 1933, as
amended, or the rules and regulations of the Securities and Exchange Commission
issued thereunder, with respect to any part of the Registration Statement.

                                                     Sincerely,

                                                     /s/ MAYER, BROWN & PLATT