Compressed natural gas is a substitute for gasoline, Diesel or LPG. CNG is made by compressing natural gas which is mainly composed of methane.
CNG is used as fuel in internal combustion engine cars that have been converted into bi-fuel vehicles . Natural gas vehicles are much used in the Asia-Pacific region especially Pakistan, India , Latin America, Europe, and North America due to rising gasoline prices.
Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other because natural gas is lighter than air, and disperses quickly when released. CNG may also be mixed with biogas, produced from landfills or wastewater, which doesn't increase the presence of carbon in the atmosphere.
In response to high fuel prices and environmental concerns, CNG is starting to be used also in tuk-tuks and pickup trucks, transit and school buses, and trains.
CNG's volumetric energy density is about 42% that of liquefied natural gas (because it is not liquefied), and 25% of Diesel fuel.
Worldwide, there were 14.8 million natural gas vehicles by 2011, led by Iran with 2.86 million, Pakistan (2.85 million), Argentina (2.07 million), Brazil (1.7 million), and India (1.1 million).
Several manufacturers sell bi-fuel cars.Any existing gasoline vehicle can be easily converted to a bi-fuel (gasoline/CNG) vehicle.