Gas, gaseous fuel, not to be confused with gasoline, which is a liquid fuel often referred to as gas. An important energy source for homes, institutions, and industries, gas is used to heat and cool buildings, cook, heat water, and create steam. Chemicals in gas are used to produce plastics, drugs, and cleansers. Gas is used to create many products, such as metals, paper, fabrics, glass, and cement. Two kinds of gas exist: natural and manufactured. Natural gas is found by drilling into a gas deposit in the earth; manufactured gas is created by processing coal or petroleum. The U.S. is a leading natural gas producing country and has nearly 2 million miles (3,200,000 km) of gas pipeline through which gas is transmitted and distributed. Because the use of gas does not create much air pollution, scientists are trying to develop ways in which it can be used as a transportation fuel to power cars, trucks, and ships.