What Is Natural Gas?

Natural gas is a fossil fuel consisting primarily of methane (CH4), with smaller fractions of ethane, propane, butane, and trace non-hydrocarbon gases including carbon dioxide, nitrogen, and hydrogen sulfide. It forms over geological timescales from the decomposition of organic matter under pressure and heat, accumulating in porous rock formations or in association with crude oil deposits. Natural gas is one of the most widely used energy resources in the world, serving as a fuel for electricity generation, industrial heating, and residential applications, and as a chemical feedstock for fertilizers and plastics.

As an energy carrier, natural gas occupies a transitional position in global energy systems. It produces fewer carbon dioxide emissions per unit of energy than coal or fuel oil when combusted, a characteristic that has led to its expanded use as a lower-emission complement to variable renewable sources such as wind and solar power. The U.S. Energy Information Administration reports that natural gas supplied approximately one-third of total U.S. primary energy in recent years, making it the single largest energy source in the American mix.

Composition and Physical Properties

Raw natural gas extracted from a well requires processing before commercial use. Processing facilities remove water vapor, hydrogen sulfide, and carbon dioxide, then fractionate the heavier hydrocarbons (ethane, propane, and butane) as natural gas liquids (NGLs), which are sold as separate products. The processed pipeline-quality gas is predominantly methane, with a heating value of approximately 1,010 British thermal units per standard cubic foot. Liquefied natural gas (LNG) is produced by cooling processed gas to approximately negative 162 degrees Celsius, which reduces its volume by a factor of roughly 600 and enables ocean transport by cryogenic tanker to markets without pipeline access.

Extraction and Hydraulic Fracturing

Natural gas is extracted from both conventional reservoirs, where it migrates into porous sandstone or carbonate formations, and unconventional formations such as shale, tight sands, and coalbed methane seams. The development of horizontal drilling combined with hydraulic fracturing (fracking) unlocked vast reserves in shale formations across North America beginning in the 2000s, producing a significant shift in global gas supply. In hydraulic fracturing, a pressurized mixture of water, sand, and chemical additives is injected into a wellbore to fracture the rock and prop open the resulting fractures, allowing gas to flow. Research published on integrated electricity and gas systems planning highlights how expanded unconventional gas production has altered the economics of gas-fired power generation and grid planning.

Role in Electric Power Systems

Gas-fired power plants occupy a strategic role in electric power grids because of their operational flexibility. Combined-cycle gas turbine (CCGT) plants achieve thermal efficiencies above 60 percent and can ramp output quickly, making them well suited for balancing intermittent renewable generation. Peaker plants, typically simple-cycle gas turbines, provide fast-start capacity for peak demand periods. IEEE research on the impact of natural gas infrastructure on electric power systems identifies the interdependence between gas pipeline capacity and generator dispatch as a source of system risk, particularly when pipeline constraints limit fuel delivery during cold weather events.

Applications

Natural gas has applications in a range of fields, including:

• Electricity generation through combined-cycle and peaker gas turbine plants
• Residential and commercial space heating and cooking
• Industrial process heat for manufacturing, cement production, and chemical processing
• Feedstock for ammonia synthesis in fertilizer production and for hydrogen production
• LNG export and maritime fuel, including as a lower-emission ship propellant