The Clean Air Act Clean Alternative Fuels Specified in the Clean Air Act Amendments of 1990 Include Compressed Natural Gas Natural gas is composed mostly of methane. Although it can be liquefied, it is most commonly used in transportation vehicles in a compressed, gaseous form.
Natural gas has many advantages for use as a vehicular fuel.
First, there is a large domestic resource, as the United States is one of the world's largest producers of natural gas. Second, establishing a fuel-delivery system for fleets could be relatively straightforward. Existing municipal gas lines could supply compressing stations, where the gas would in turn be delivered to vehicles. Disadvantages include a shorter distance traveled per tank of fuel and potentially higher NO x emissions than those from gasoline. For fleet operators, the large size of the gas tank is an important consideration.