According to the Natural Gas Vehicle Coalition (NGVC), as of 2004 there are 130,000 light- and heavy-duty compressed natural gas (CNG) and liquefied natural gas (LNG) vehicles in the United States and 2 million worldwide.
Dedicated natural gas vehicles (NGVs) are designed to run only on natural gas; bi-fuel NGVs have two separate fueling systems that enable the vehicle to use either natural gas or a conventional fuel (gasoline or diesel). In general, dedicated NGVs demonstrate better performance and have lower emissions than bi-fuel vehicles because their engines are optimized to run on natural gas. In addition, the vehicle does not have to carry two types of fuel, thereby increasing cargo capacity and reducing weight.
There are a few light-duty NGVs still available, but if you want a specific type of vehicle, you may want to consider retrofitting a vehicle to an NGV by using an aftermarket conversion system. Heavy-duty NGVs are also available as trucks, buses, and shuttles. Approximately one of every five new transit buses in the United States is powered by natural gas.
As a new twist, tests are being conducted using natural gas vehicles that are fueled with a blend of compressed natural gas and hydrogen. For more information on CNG/hydrogen blends, please see the page on HCNG.