Okla. Stat. tit. 47, § 153

It shall be unlawful for any person to drive any state-owned or -leased automobile at any time and for any purpose, on any street or highway within this state, unless the provisions of Section 151 of this title have been strictly complied with, provided, however, the Commissioner of the Department of Public Safety is hereby authorized to set aside automobiles for use by the Department so that the same may be available to the Department without identifying marks thereon. These vehicles shall not be used for traffic enforcement on a routine basis.