natural gas, natural mixture of gaseous hydrocarbons found issuing from the ground or obtained from specially driven wells. The composition of natural gas varies in different localities. Its chief component, methane, usually makes up from 80% to 95%, and the balance is composed of varying amounts of ethane, propane, butane, and other hydrocarbon compounds. Some of the hydrocarbons found in gasoline also occur as vapors in natural gas; by liquefying these hydrocarbons, gasoline can be obtained.
Although commonly associated with petroleum deposits it also occurs separately in sand, sandstone, limestone, and shale deposits. Some geologists theorize that natural gas is a byproduct of decaying vegetable matter in underground strata, while others think it may be primordial gases that rise up from the mantle. Because of its flammability and high calorific value, natural gas is used extensively as an illuminant and a fuel.
Natural gas was known to the ancients but was considered by them to be a supernatural phenomenon because, noticed only when ignited, it appeared as a mysterious fire bursting from the ground. One of the earliest attempts to harness it for economic use occurred in the early 19th cent. in Fredonia, N.Y. Toward the latter part of the 19th cent., large industrial cities began to make use of natural gas, and extensive pipeline systems have been constructed to transport gas. Since the late 20th cent., improvements in hydraulic fracturing, or "fracking"—in which pressurized fluids are injected into a well to induce rock fractures that allow the release of natural gas—and its use in combination with horizontal drilling has permitted natural gas to extracted from previously untappable deposits of shale.
Liquefied natural gas, or LNG, is natural gas that has been pressurized and cooled so as to liquefy it for convenience in shipping and storage. The boiling point of natural gas is extremely low, and only in the 1970s did cryogenic technology (see low-temperature physics) advance enough to make the production and transport of LNG commerically feasible. Some of the natural gas moved to and from the United States is carried as LNG in special tankers.
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