
For the fifth consecutive year the American Council for an Energy-Efficient Economy (ACEEE) has named the natural gas-fueled Honda Civic GX the "greenest vehicle of the year." The Civic GX, which Honda says has the cleanest internal combustion engine on the market, is not well known even among auto enthusiasts

This is largely because it is available to consumers only in New York, Utah and California, though businesses in any part of the country can buy them for their fleets. Except for the fact that it runs on natural gas - and not gasoline - the 2009 Honda Civic GX sedan is little different than the four-door Civic LX

Natural gas comes out of the ground as, well, a gas. Sometimes it is found along with liquid petroleum, while other times it's in deposits by itself. After it's refined, it is mainly methane. It's possible to produce methane gas from decaying organic matter or coal, but both cost more than conventional natural gas

To be stored in an amount needed to produce useful cruising range, it must be compressed to about 3600 pounds per square inch. That's about 120 times the pressure in your tires. It's also why it's commonly referred to as CNG for "compressed natural gas.

Natural gas has several major benefits as a fuel for Americans. First, it is accepted as the cleanest-burning fossil fuel: Honda says the Civic GX burns some 90 percent cleaner than an equivalent gasoline-fueled vehicle. Also, it produces 75 percent fewer NOx pollutants (oxides of nitrogen) compared to a gasoline engine