Bi-fuel vehicles are different from flex-fuel vehicles. A bi-fuel vehicle has two separate fuel storage and delivery mechanisms. One type of fuel storage may be for gasoline or diesel while the other type may be for CNG or LPG. A vehicle that could run on gasoline and LPG would be considered a bi-fuel vehicle. Even though CNG and LPG are fossil fuels, they are much cleaner burning than gasoline or diesel. Automotive manufacturers are producing bi-fuel (CNG and gasoline) vehicles to encourage the use of the domestic supply of natural gas as gasoline prices continue to rise.