Those contracts are unlawful which are:
1. Contrary to an express provision of law.
2. Contrary to the policy of express law, though not expressly prohibited; or, 3. Otherwise contrary to good morals.
Okla. Stat. tit. 15, § 211
What contracts are unlawful
R.L.1910, § 972.
Official source: Oklahoma Legislature. Reproduced from public-domain Oklahoma statutes; confirm against the official source for the current text. Not legal advice.