A single barrel of crude oil is equivalent to 42 gallons. On average, refineries can convert a single 42-gallon barrel of oil into either 12 gallons of diesel fuel, 4 gallons of jet fuel or 19 gallons of gasoline.
The 42-gallon standard for a barrel of oil was adopted officially in 1866 when a group of U.S. oil producers gathered in Titusville, Pennsylvania. Even before this meeting, the 42-gallon watertight tierce was used as a standard shipping container. The tierce could contain anything from fish to soap or molasses. The crude oil that fills today's barrel can be refined or made into diesel, gasoline, jet fuel, asphalt and liquefied petroleum gas.