Okla. Stat. tit. 47, § 47-1-173.1: Tank vehicle

Tank Vehicle.

Any commercial motor vehicle designed to transport any liquid or

gaseous materials within a tank or tanks having an individual rated

capacity of more than one hundred nineteen (119) gallons and an

aggregate rated capacity of one thousand (1,000) or more gallons

that is either permanently or temporarily attached to the vehicle or

the chassis. A commercial motor vehicle transporting an empty

storage container tank, not designed for transportation, with a

rated capacity of one thousand (1,000) or more gallons that is

temporarily attached to a flatbed trailer is not considered a tank

vehicle. Such vehicles include but are not limited to cargo tanks

and portable tanks as defined by 49 C.F.R., Part 171; provided, a

commercial motor vehicle transporting an empty storage container

tank, not designed for transportation, with a rated capacity of one

thousand (1,000) or more gallons that is temporarily attached to a

flatbed trailer is not considered a tank vehicle.