In fuel, a bobtail is a delivery truck with the tank built onto the truck itself, with no separate trailer behind it.
The bobtail is the local delivery truck of the trade. It carries a smaller load and handles the short runs, out to gas stations, farms, homes, and job sites.
It works as the partner to the big transport trailer. The transport hauls large volumes over long distances, and the bobtail breaks that fuel into the smaller deliveries a customer actually takes.
In useA transport drops a full load at the bulk plant, and the bobtail runs it out to a dozen farms a few hundred gallons at a time.
Where the word comes from
Bobtail means a short or cut-off tail, an old word once used for a horse or animal with a docked tail. Truckers borrowed it for a truck running with no trailer, and the fuel trade uses it for the short, tank-on-the-body delivery truck.
See also Transport, Bulk plant