Okla. Stat. tit. 74, § 500.8

A per diem in an amount authorized by the federal Government Services Administration (GSA) in its Federal Travel Regulation (FTR) 42 C.F.R. Section 300-1.1 et seq. and as updated in its FTR Bulletins is authorized while in travel status. In computing per diem reimbursement a day shall be a calendar day. The first and last days of travel shall be paid at a rate of seventy-five percent (75%) of the full-day per diem. Provided, however, that no per diem shall be made for periods which do not include overnight status. If meals and lodging at a meeting, workshop, conference or other object of travel are furnished as a "package plan", reimbursement may be made, based upon a receipt, but at a daily rate of not to exceed the total daily rate provided in this act.