Okla. Stat. tit. 12A, § 12A-2A-202: Final expression; parol or extrinsic evidence

FINAL EXPRESSION; PAROL OR EXTRINSIC EVIDENCE

Terms with respect to which the confirmatory memoranda of the

parties agree or which are otherwise set forth in a record intended

by the parties as a final expression of their agreement with respect

to such terms as are included therein may not be contradicted by

evidence of any prior agreement or of a contemporaneous oral

agreement but may be explained or supplemented:

(a) by course of dealing or usage of trade or by

course of performance; and

(b) by evidence of consistent additional terms

unless the court finds the record to have been intended also as a

complete and exclusive statement of the terms of the agreement.