Vehicles that run on natural gas instead of gasoline are called natural gas vehicles (NGVs). There are about 175,000 NGVs on U.S. roads today and more than 23 million worldwide. NGVs are a popular transportation choice because they run cleaner than other vehicles. Compared to gasoline- or diesel-powered vehicles, they produce much lower levels of pollutants and cost less to maintain. Also, natural gas costs less than conventional gasoline at the pump.