Natural Gas as Auto Fuel

Compared to gasoline, compressed natural gas (CNG) is cleaner, less expensive, and generally comes from domestic reserves. However, CNG vehicles also require some compromises, including the use of a special refueling infrastructure that is not widely developed in the United States.

CNG vehicles store natural gas in pressurized tanks and burn the gas in slightly modified internal combustion engines. Natural gas, which is 90 percent methane, has a much higher octane rating than gasoline, allowing for higher compression ratios and therefore greater efficiency in the engines that use it. Natural gas burns so cleanly that CNG vehicles rival hybrids in producing extremely low levels of smog-forming pollutants. However, CNG vehicles tend to have higher greenhouse gas emissions than hybrids.