Semi truck fuel tanks vary in size, but they hold an average of 125 to 300 gallons of fuel. There is a fuel tank located on each side of the tractor, and fuel is distributed between the two tanks to balance weight.
Fuel tanks on semi trucks are not standard but are specialized to the buyer's needs. For example, a 2011 Kenworth T660 truck can be purchased previously-owned with dual 120-gallon fuel tanks for 240 total gallons. Tractors carrying larger fuel tanks are ideal for cross-country drivers or drivers of trucks carrying lots of weight. Some truck manufacturers put larger fuel tanks on one side over the other for balance.