Natural gas is a nonrenewable source of energy used primarily for heating and generating electricity. The U.S. produces natural gas from wells within the U.S. but also imports natural gas from abroad. The U.S. imports natural gas via pipeline from Canada and Mexico, but to move natural gas from countries that are further away, the natural gas is turned into a liquid (also called "Liquefied Natural Gas" or LNG) by supercooling and transported as a liquid on tankers before being warmed up and turned into a gas upon arrival in the United States.
Natural gas also has become increasingly popular as an alternative transportation fuel. Serving alternative fuel vehicles, natural gas is clean burning and produces significantly fewer harmful emissions than reformulated gasoline. Natural gas can either be stored on board a vehicle in tanks as compressed natural gas (CNG) or cryogenically cooled to a liquid state, liquefied natural gas. (Source: DOE, EIA / Photo: Flickr)