Exhibit 10.1 SUPPLEMENTAL AGREEMENT TO AMENDED AND RESTATED AGREEMENT AND PLAN OF MERGER This supplemental agreement (this "Supplement") dated as of July 8, 1999 relates to the Amended and Restated Agreement and Plan of Merger dated as of May 19, 1999 (the "Agreement") by and among Devon Energy Corporation, an Oklahoma corporation ("DVN"), Devon Delaware Corporation, a Delaware corporation and a direct, wholly owned subsidiary of DVN ("Newco"), Devon Oklahoma Corporation, an Oklahoma corporation and a direct, wholly owned subsidiary of Newco ("Devon Oklahoma"), and PennzEnergy Company, a Delaware corporation ("PZE"). Any capitalized terms used herein without definition shall have the meaning assigned thereto in the Agreement. In furtherance of and to facilitate the preparation and filing of a registration statement on Form S-4 of Newco, a portion of which will also serve as the joint proxy statement with respect to the meetings of the stockholders of DVN and of PZE in connection with the Merger, DVN, Newco, DVN Oklahoma and PZE hereby supplementally agree as follows: 1. The By-Laws of Newco at the Effective Time shall be as set forth in Exhibit A to this Supplement. 2. The committees of the Board of Directors of Newco at the Effective Time shall be as set forth in Exhibit B to this Supplement. 3. The Rights Agreement of Newco at the Effective Time shall be substantially as set forth in Exhibit C to this Supplement. 4. The person designated by PZE under Section 3.1 of the Agreement for the Board of Directors of Newco to be mutually approved by the chairman of PZE and the president of DVN shall be William J. Johnson. The Agreement shall continue in full force and effect in accordance with the provisions thereof. IN WITNESS WHEREOF, the parties have executed this Supplement and caused the same to be duly delivered on their behalf on the date and year first written above. DEVON ENERGY CORPORATION By: /s/ J. Larry Nichols ----------------------------- J. Larry Nichols President DEVON DELAWARE CORPORATION By: /s/ J. Larry Nichols ----------------------------- J. Larry Nichols President DEVON OKLAHOMA CORPORATION By: /s/ J. Larry Nichols ----------------------------- J. Larry Nichols President PENNZENERGY COMPANY By: /s/ James L. Pate ----------------------------- James L. Pate Chairman of the Board Exhibit A [See Exhibit 3.3 of the Registration Statement on S-4 of Devon Delaware Corporation dated July 15, 1999] Exhibit B Newco Committees of the Board of Directors Audit (3 persons) Ferguson (Chair) 1 additional former DVN director designated by DVN 1 former PZE director designated by PZE Compensation (4 persons) Gavrin (Chair) 1 additional former DVN director designated by DVN 2 former PZE directors designated by PZE Nominating (4 persons) Gellert (Chair) 1 additional former DVN director designated by DVN 2 former PZE directors designated by PZE Executive (2 persons) Nichols Pate (Chair) Exhibit C [See Exhibit 4.2 of the Registration Statement on Form S-4 of Devon Delaware Corporation dated July 15, 1999]