Okla. Stat. tit. 61, § 113.1v2

A. A public construction contract shall provide for partial payment based upon work completed. The contract shall provide that up to five percent (5%) of all partial payments made shall be withheld as retainage. At any time the contractor has completed in excess of fifty percent (50%) of the total contract amount, the retainage shall be reduced to two and one-half percent (2.5%) of the amount earned to date once the public agency has determined that satisfactory progress is being made. B. The Department of Transportation or the Oklahoma Turnpike Authority shall not withhold retainage on public construction contracts awarded by the Department or the Authority. C. The Department of Transportation shall not withhold retainage or require any bond on projects awarded to railroads on the railroad's privately owned or operated rail property.