A contract not in writing may be altered in any respect by consent of the parties, in writing, without a new consideration, and is extinguished thereby to the extent of the new alteration.
Okla. Stat. tit. 15, § 236
Oral contract may be altered by writing - Extinguishment in part
R.L.1910, § 987.
Official source: Oklahoma Legislature. Reproduced from public-domain Oklahoma statutes; confirm against the official source for the current text. Not legal advice.