They are the major source of energy for automobiles, airplanes, and other vehicles. In addition, liquid fuels are used to heat buildings. Petroleum, also called crude oil, ranges from clear yellow-brown oils to thick, black tars. Some crude oil is burned as fuel in stoves and boilers without processing. However, most petroleum is refined to produce such fuels as gasoline, diesel oil, and kerosene.
Gasoline is used to provide energy for most motor vehicles and piston-engine airplanes.
Diesel oil powers most trains, ships, and large trucks. Kerosene provides energy for jet airplanes. Other fuel oils obtained by refining petroleum include distillate oils and residual oils. Distillate oils are light oils, which are used chiefly to heat homes and small buildings. Residual oils are heavy, thick oils.