Okla. Stat. tit. 62, § 62-34.72: Procedure for payment of interest

The Director of the Office of Management and Enterprise Services

shall establish a procedure to assess and pay interest for the late

payment of an invoice, which interest shall be calculated beginning

the thirtieth day after receipt by the designated office of a proper

invoice for which payment has not been mailed, transmitted, or

delivered to a vendor by the close of business on the forty-fifth

day. Such interest shall be at an annualized rate based on an

average of the interest rate for thirty-day time deposits of state

funds during the last calendar quarter of the last preceding fiscal

year, as reported by the State Treasurer.