Okla. Stat. tit. 62, § 57.312

The State Treasurer shall invest all sinking fund monies in direct obligations of the United States of America or in certificates of deposits from banks in the State of Oklahoma acceptable as depositories by the State Treasurer when such certificates of deposits are secured by acceptable collateral and yield as much or more than direct obligations of the United States of America, to mature in time to meet the principal and interest payments on the Oklahoma Building Bonds of 1992. Such earnings shall be deposited in the sinking fund, except that any funds received pursuant to a contract entered into by the Office of the State Treasurer for the investment of revenues dedicated for bond repayment may be deposited in the Special Cash Fund of the State Treasury.