Okla. Stat. tit. 47, § 47-1-183: Truck tractor

(a) Every motor vehicle designed and used primarily for drawing

other vehicles and not so constructed as to carry a load other than

a part of the weight of the vehicle and load so drawn; and

(b) For the purposes of paragraph 3 of subsection (c) of

Section 14-103 of this title, the term truck-tractor shall also

include oil field rig-up trucks when towing a trailer or

semitrailer.