Okla. Stat. tit. 69 § 1512
No obligation shall be incurred by the Department of Transportation against the State Highway Construction and Maintenance Fund during any fiscal year in excess of the total amount of monies accruing to said fund during such fiscal year. Construction contracts and purchase orders issued by the Department of Transportation, setting forth the actual or estimated cost of construction as consideration for the cost of work to be done or services, supplies and equipment to be furnished, shall constitute obligations within the meaning of this act. Monthly, bimonthly or weekly payrolls of the Department of Transportation shall constitute current charges and shall become obligations against the State Highway Construction and Maintenance Fund at the time the payrolls are filed with the Director of the Office of Management and Enterprise Services for payment.
Okla. Stat. tit. 69, § 1512