Natural gas is a mixture of light, gaseous hydrocarbons, consisting primarily of methane, the lightest gas in the mixture. It's exact composition varies, but nitrogen and sulfur compounds are present in much lower concentrations than in the other fossil fuels, coal and petroleum. Thus, natural gas burns with much less pollution and greater efficiency than coal or petroleum and is becoming the fossil fuel of choice for the production of electrical power.

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Transportation of natural gas by means other than pipelines requires that the gas be liquefied to conserve space and make transportation economically viable. When natural gas is cooled to about -260 degrees Fahrenheit it is liquid and has a volume about 600 times less than in the gaseous state. In liquid form it is suitable for both transportation and storage.

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Shale gas is a form of "unconventional" natural gas. It is not easily extracted from the depths at which it is found. In fact its deposits are normally buried 15,000 feet or more underground. Special procedures that involve more than just drilling and simple extraction processes are needed to reach the gas, which is extracted by a combination of horizontal drilling and hydraulic fracturing (otherwise known as "fracking") of the sedimentary shale in which the natural gas is entrapped. These two processes have made possible the economical extraction of massive amounts of shale gas that it otherwise would not have been feasible to obtain.

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As a source of energy, natural gas releases far fewer pollutants and greenhouse gases than either oil or coal. Most natural gas recovery in the USA, until recently, has been from natural, underground reservoirs, using processes similar in many ways to those used in the extraction of oil. Indeed, many reservoirs tapped for oil contain natural gas.

However, recent development of processes for economical extraction of natural gas from shale formations have increased public concern about the environmental effect of those processes. Those concerns include the overuse and contamination of water tables, land misuse, threat to endangered species and other environmental problems.

Additionally, methane, of which natural gas is almost entirely composed, is a gas with a greenhouse warming effect several times that of carbon dioxide. Leakage of methane into the atmosphere is a potential problem in its impact on the global climate and must be carefully monitored in any natural gas extraction process.

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The natural gas industry consists of a variety of entities with differing functions. Following is a simplified listing of the types of companies that constitute the makeup of the natural gas industry:

Producers

These are the owners and developers of natural gas wells. They can range from giant corporations to one or two person well owners.

Processing

Processing corporations are comparable to refinery companies in the oil industry. They separate the natural gas taken from earth into its marketable components, mostly methane.

Pipelines

Pipeline companies transport processed natural gas to locales where it can be stored and later marketed.

Storage

Storage operators own and control numerous underground storage facilities for natural gas. The gas is stored for later marketing and, in some cases, as safeguards to be used in emergencies.

Marketing

Marketing companies facilitate connections between those entities in the industry that produce, process, transport and store natural gas and the retailers and end users who purchase the final, delivered products.

Local Distribution Companies (LDC)

LDC's bring natural gas to the end users via local pipelines.

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