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.
Okla. Stat. tit. 62, § 34.72