This excerpt taken from the EOG 10-Q filed Apr 30, 2007.
SECTION 15. AMENDMENT AND WAIVER.
No provision of this Agreement may be amended or waived (whether by act or course of conduct or omission or otherwise) unless that amendment or waiver is by written instrument signed by the parties hereto. No waiver by either party of any breach of this Agreement shall be deemed a waiver of any other or subsequent breach.