Okla. Stat. tit. 57, § 535

Where there is more than one grade within a specific occupational class, as authorized in Section 11 of this act, the Director of the Department of Corrections, each warden or each superintendent is authorized to fill a designated grade in the next lower authorized grade, provided the total number of employees in the specific occupational class does not exceed the total number of employees authorized for all grades of that specific occupational class.