The comparisons I have made in this presentation have been primarily for a conventional gasoline vehicle versus a compressed natural gas vehicle. However, similar reductions come from the use of liquefied natural gas. In addition to tailpipe emission benefits from natural gas, the total life cycle emissions of natural gas, including resource extraction, processing, conversion, transportation, and distribution, are far less than petroleum based transportation fuels.
Propane can also result in tailpipe emission benefits similar to a compressed natural gas.
Both ethanol and methanol are also considered alternative fuels, however there is currently insufficient production of these fuels for them to be considered a viable alternative, and from an environmental standpoint, the benefits of these fuels is minor. Electric vehicles are considered zero emission vehicles and result in the greatest environmental benefits. While the application of electric vehicles is limited by range and recharging needs, in some situations they are the perfect solution.