Okla. Stat. tit. 62, § 57.131

Any bank, trust or insurance company organized under the laws of Oklahoma may invest its capital, surplus and reserve funds and other funds under its control in bonds issued under the provisions of this act. The officers having charge of any fund of the State of Oklahoma, or any department, agency, or institution thereof or any sinking fund of any county, city, town, township, board of education or school district may invest such funds in bonds issued under the provisions hereof. Such bonds shall also be approved as collateral security for the deposit of any public funds and for the investment of trust funds.