Natural gas is made up primarily of methane with trace amounts of other gases. It occurs naturally underground and is extracted through gas wells or in conjunction with crude oil production. For storage purposes it can be stored as compressed natural gas (CNG) or liquid natural gas (LNG).
Natural gas vehicles (NGV) are the most advanced alternative fuel technology available commercially. Both light and heavy-duty vehicles can use CNG. According to the Natural Gas Vehicle Coalition, more than 20% of new transit bus orders are for natural gas buses. Some vehicles come already equipped to run either entirely on CNG (dedicated) or on both CNG and gasoline or diesel (bi-fuel). Additionally, many vehicles can be converted to run on CNG. All U.S.-based, full-sized transit bus manufacturers offer CNG buses. Applications include transit and school buses, refuse trucks, light-duty vehicles, vans, passenger cars and taxis. LNG is not suitable for light-duty vehicles but is an ideal fuel for large (class 8) trucks, transit buses, and medium-duty fleet trucks. There are over 150,000 NGVs on the road in the U.S. fueling at 1,500 locations. Over half of these sites are commercially accessible.