This 20-CFM to 250-CFM 125-psi Air Compressor is measured in HP (Horsepower) and CFM (cubic feet of air per minute). The gallon size of the tank tells you how much compressed air "in reserve" is available. Diesel powered compressor is widely used in remote areas with problematic access to electricity. It is noisy and require ventilation for exhaust gases. This unit can be powered by Diesel Fuel or by Electric.