Okla. Stat. tit. 74, § 500.15

All claims for reimbursement of travel expenses shall be submitted on the regular authorized form of travel expense claim, and shall be approved by the official or employee performing the travel, and approved by the official or employee designated in Section 34.68 of Title 62 of the Oklahoma Statutes, for the agency in which the employee works. Receipts may be provided to the Office of Management and Enterprise Services in electronic form.