Alternatives to gasoline usually focus on ethanol, electricity or hybrids. But two forms of natural gas also are currently used in vehicles: compressed natural gas (CNG) and liquefied natural gas (LNG). Both are domestically produced, relatively low priced and commercially available. CNG and LNG are sold in units of gasoline or diesel gallon equivalents (GGEs or DGEs) based on the energy content of a gallon of gasoline or diesel fuel.
CNG is produced by compressing natural gas to less than 1% of its volume at standard atmospheric pressure. LNG is natural gas in its liquid form. LNG is produced by purifying natural gas and super-cooling it to minus 260 F to turn it into a liquid. LNG must be kept at cold temperatures and is stored in double-walled, vacuum-insulated pressure vessels. LNG is suitable for trucks that require longer ranges because liquid is denser than gas and, therefore, more energy can be stored by volume.
There are fewer than 200 LNG filling stations in the United States.
Most CNG vehicles are sold to companies that operate large fleets of them. Fleet applications are ideal for CNG since fleet vehicles tend to drive predictable routes and can refuel where they are stored. According to the Alternative Fuels Data Center, as of March 2022, there are about 175,000 vehicles on American roads powered by natural gas.
The main disadvantage of natural gas for the average driver is that filling stations are scarce: about 1,600 nationwide as of January 2023, according to Natural Gas Vehicles for America, and dedicated to the development of vehicles powered by natural gas or biomethane. LNG options are more scarce, with only about 140 stations nationwide, according to NVGA, and filling up takes considerably longer than standard liquid fuels.
It is possible to convert nearly any car to run on CNG, though the process is expensive and must be done by a certified installer. Although Congress encourages CNG conversion by offering tax incentives, the conversion needs an EPA certification to qualify.