In 1930, Roy Gilbert Sr. started Gilbert Truck Line in Cotulla, TX with one used truck serving San Antonio, TX to Cotulla, TX. During 1940, He was able to secure authority to serve Laredo and the Mexican border. Through the 1940’s, the fleet grew to about 50 pieces of equipment. In 1950, Mr. Gilbert purchased Southwestern Motor Transport Inc., and merged the two companies. This brought the fleet to just over 100 units.
Deregulation in 1981 allowed S.M.T. to extend service to surrounding states, the Midwest, and the Southeast.