Okla. Stat. tit. 19, § 164

When transportation involves the use of the private automobile of a county officer, deputy, or county employee entitled to reimbursement, such county officer, deputy or employee shall be entitled to claim reimbursement for use thereof at the rate provided for in the State Travel Reimbursement Act for state officers and employees. Official duties shall include attendance by a county officer and at least one of his deputies for voluntary instruction.