Compressed Natural Gas (CNG) is a substitute for gasoline (petrol), diesel, or propane fuel. It is considered to be an environmentally "clean" alternative to those fuels and it is much safer than other motor fuels in the event of a fuel spill: natural gas is lighter than air, so it disperses quickly when leaked or spilled. It is made by compressing natural gas (which is mainly composed of methane (CH 4 )), by about 75%. It is stored and distributed in hard containers, at a normal pressure of 200–220 bar (20–22 MPa), usually in cylindrical or spherical shapes to maintain equal pressure on the walls of the containers.

In response to high fuel prices and environmental concerns, compressed natural gas is starting to be used in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks, and in transit and school buses.