All fossil fuels produce CO2, but of those fuels, natural gas produces the least. Often found in the same deposits as oil, it was, like oil, formed from the remains of ancient organisms subjected to millions of years of heat and pressure. Natural gas produces 30 percent less CO2 than petroleum and about 45 percent less CO2 than coal for an equivalent amount of energy. Currently, natural gas provides about a quarter of the world's energy supply.
Natural gas turns to a liquid when chilled to very low temperatures—about -162°C (-260°F)—and can be shipped in special insulated, double-hulled vessels. Large natural gas deposits exist in the Middle East, Asia, and North America.