Okla. Stat. tit. 36, § 2617

Every corporation doing business pursuant to this article is hereby declared to be a not-for-profit institution and to be exempt from state, county, district, municipal and school tax, including the taxes prescribed by this Code, and excepting only the fees prescribed by Article 3 of the Insurance Code (Insurance Department and Insurance Commissioner), the premium tax levied pursuant to Article 6 of the Insurance Code (Authorization of Insurers and General Requirements), and taxes on real and tangible personal property situate within this state.