High Quality Content by WIKIPEDIA articles! Bi-fuel vehicles are vehicles with multifuel engines capable of running on two fuels. On internal combustion engines one fuel is gasoline or diesel, and the other is an alternate fuel such as natural gas (CNG), LPG, or hydrogen. The two fuels are stored in separate tanks and the engine runs on one fuel at a time, unlike flexible-fuel vehicles ("dual-fuel"), that store the two different fuels mixed together in the same tank, and the resulting blend is burned in the combustion chamber. Bi-fuel vehicles have the capability to switch back and forth from gasoline or diesel to the other fuel, manually or automatically.