Okla. Stat. tit. 43, § 130

Upon the trial of an action for a divorce, or for alimony the court may admit proof of the admissions of the parties to be received in evidence, carefully excluding such as shall appear to have been obtained by connivance, fraud, coercion or other improper means. Proof of cohabitation, and reputation of the marriage of the parties, may be received as evidence of the marriage. But no divorce shall be granted without proof.