Okla. Stat. tit. 74, § 500.4

A. Authorized persons traveling on official state business within the State of Oklahoma may utilize railroads, airplanes, buses, whether intracity or intercity, or other public conveyance. Reimbursement for fares paid for airplane transportation shall not exceed coach class fare except as provided herein. Reimbursement for fares paid for airplane transportation may be at the business class fare rate for international travel. Other public conveyance fares shall not exceed the lesser of the normal charge or coach class airplane fare. Taxicab or rideshare fares within the State of Oklahoma and communication charges may be reimbursed only upon justification as to the necessity for their use. B. Agency heads or their authorized designees may approve the use of motor vehicles for official travel within the State of Oklahoma. If available, agency owned motor vehicles or motor vehicles leased from the State Motor Pool, either on a full-time basis or for individual trips, shall be utilized for such travel. Reimbursement for use of privately owned motor vehicles may be authorized by the agency head. C. Reimbursement for authorized use of privately owned motor vehicles shall not exceed the amount prescribed by the Internal Revenue Code of 1986, as amended, or rules, procedures or other action by the Internal Revenue Service, for use in determining the standard mileage rate allowed for a business expense deduction. Distances for which reimbursement for use of privately owned motor vehicles is claimed shall be actual business miles based on a recognized Global Positioning System (GPS) or based on map and vicinity business mileage.