Fuels
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Natural Gas

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Natural gas can be used in any vehicle with an internal-combustion engine, although the vehicle must be outfitted with a special carburetor or fuel injector and fuel tanks. Natural gas costs less than gasoline and has a higher octane rating. About 114,000 cars, trucks, and buses run on natural gas in the United States.

Because of its gaseous nature, natural gas must be compressed or liquefied to be efficiently stored on board a vehicle. Compressed natural gas (CNG) tanks have to be refilled more often than gasoline tanks, and there are few refueling stations.

Liquefied natural gas (LNG) is made by cooling natural gas to a temperature of -259°F. At that temperature, natural gas becomes a liquid, and its volume is reduced 615 times, which makes it easier to store and transport.

Figure 9
Natural gas liquids
At the wellhead, natural gas typically contains about 92 percent methane and 8 percent natural gas liquids.

Figure 9. Natural gas liquids. At the wellhead, natural gas typically contains about 92 percent methane and 8 percent natural gas liquids.