Not all vehicle fuels are liquids. Some are gaseous fuels, such as natural gas, hydrogen, and blends of the two. Gaseous fuels must be stored in the vehicle in a pressurized tank. Two types of natural gas can be used: compressed natural gas (CNG) and liquefied natural gas (LNG).
Dedicated natural gas vehicles run only on natural gas. Bifuel natural gas vehicles have two separate fueling systems, which allows them to use either natural gas or petroleum. Unlike natural gas, hydrogen transportation fuel is still in early stages of development. Pure hydrogen has been used effectively in some vehicles with internal combustion engines when the fuel is mixed with natural gas. Hydrogen fuel cell vehicles are still being developed.
Learn more about gaseous fuels.