Okla. Stat. tit. 47, § 12-403
On and after the effective date of this Code, every motor vehicle, operated singly or when towing any other vehicle, shall be equipped with a mirror so located as to reflect to the driver a view of the highway for a distance of at least two hundred (200) feet to the rear of such motor vehicle.
Laws 1961, p. 408, § 12-403.