Natural gas

Natural gas, also referred to as fossil gas, methane gas, or simply gas, is a naturally occurring mixture of gaseous hydrocarbons. Composed primarily of methane—typically around 95 per cent—it also contains smaller proportions of higher alkanes and trace quantities of gases such as carbon dioxide, nitrogen, hydrogen sulphide, and helium. In its pure form, methane is colourless and odourless; therefore, commercial suppliers commonly add odourants such as methanethiol to ensure that leaks can be easily detected. As the second most significant greenhouse gas after carbon dioxide, methane plays an important role in contemporary discussions on climate change.

Chemical Composition and Physical Characteristics

The principal component of natural gas is methane (CH₄), whose molecular structure allows large amounts of stored chemical energy to be released when burned. Additional components, such as ethane, propane, butanes, pentanes, and other heavier hydrocarbons, occur naturally in varying concentrations. Impurities—including hydrogen sulphide, water vapour, carbon dioxide, nitrogen, and occasionally helium—are typically removed during processing to make the gas suitable for commercial use.
Natural gas is lighter than air, with a density generally less than 0.64 g/mole (0.78 kg/m³). For comparison, pure methane possesses a density around 0.55 times that of air. Measurement is usually expressed in standard cubic metres (scm) or standard cubic feet (scf).

Formation of Natural Gas

Natural gas is formed through geological processes that occur over millions of years. Most deposits originate from the thermal decomposition of organic matter—principally marine microorganisms—buried beneath layers of sediment in oxygen-free environments. Over geological timescales, heat and pressure cause these materials to break down into hydrocarbons.
Two main formation pathways exist:

• Biogenic gas: Produced by methanogenic microorganisms acting on organic material, typically near the surface.
• Thermogenic gas: Produced at greater depths under intense heat and pressure, often associated with petroleum reservoirs.

The chemical energy stored within natural gas ultimately derives from solar energy captured by ancient organisms through photosynthesis.

Historical Development and Early Uses

Natural gas has been known since antiquity. In ancient Greece, eternal flames such as those at Mount Chimaera inspired myths about fire-breathing creatures. In ancient China around 400 BC, natural gas collected from brine-drilling operations was transported via bamboo pipelines to boil water for salt production in the Ziliujing District of Sichuan.
Prior to the twentieth century, widespread use of natural gas was limited by transportation challenges. Communities relied largely on manufactured coal gas for lighting and heating during the industrial revolution. In the United States, early European settlers observed Indigenous communities igniting natural gas seeps near Lake Erie in the seventeenth century. The first commercial natural gas well was drilled in 1821 in Fredonia, New York, eventually leading to the formation of the Fredonia Gas Light Company.
Only with the construction of extensive long-distance pipelines in the early twentieth century did natural gas become a major commercial fuel, allowing distribution far from the point of extraction.

Extraction, Processing, and Transmission

Natural gas is found in a variety of geological settings:

• Associated gas: Occurring alongside petroleum in oil fields.
• Non-associated gas: Found independently in dedicated gas fields.
• Coalbed methane: Extracted from coal seams.
• Unconventional reservoirs: Including shale gas, tight gas, sour gas, and methane hydrates.

During petroleum production, natural gas is often released as a by-product. Historically, large volumes were either vented or flared due to inadequate infrastructure, although many countries now seek to minimise flaring for environmental and economic reasons.
Before entering commercial pipelines, raw gas must undergo processing to remove impurities and separate valuable by-products. Natural gas processing may yield marketable products such as ethane, propane, butane, and natural gas liquids (NGLs). Harmful components, particularly hydrogen sulphide and carbon dioxide, are extracted through specialised treatment systems.
Transport options include:

• Pipeline transmission, the most common method.
• Liquefied Natural Gas (LNG), produced by cooling gas to sub-zero temperatures for compact, overseas transport.
• Gas-to-Liquids (GTL) technologies, which convert methane into synthetic fuels such as diesel, petrol, and jet fuel. Processes such as Fischer–Tropsch synthesis, methanol-to-gasoline (MTG), and syngas-to-gasoline plus (STG+) allow the creation of high-value liquid fuels.

Uses of Natural Gas

Natural gas is valued for its versatility. Major applications include:

• Residential heating and cooking through gas furnaces, boilers, and stoves.
• Electricity generation in gas-fired power stations, which offer rapid response times to demand fluctuations.
• Industrial energy supply for heat-intensive processes.
• Feedstock for limited chemical manufacturing, though methane is less commonly used as a raw material than other hydrocarbons.

Because natural gas burns more cleanly than coal or oil, it releases fewer toxic pollutants and produces almost no particulate matter. Its carbon dioxide emissions per unit of energy are lower than most fossil fuels, contributing to its reputation as a relatively cleaner alternative. However, the climate advantage diminishes if significant methane leakage occurs during production, processing, or transmission.

Environmental Impacts and Climate Considerations

Methane is a potent greenhouse gas, with a global warming potential many times greater than carbon dioxide over short timescales. Fugitive emissions—unintended methane leaks from wells, pipelines, and processing facilities—can offset the carbon benefits of switching from coal or oil to natural gas. Venting and flaring, although sometimes necessary for safety, contribute additional emissions and are increasingly subject to regulatory control.
Public debate has grown over the terminology used to describe the fuel. Some organisations argue that the term natural gas obscures the fuel’s climate impact and prefer fossil gas or methane gas, which more accurately reflect its environmental consequences. Studies suggest that alternative terminology may influence public perception of the fuel’s risks.

Global Distribution and Reserves

Global natural gas reserves are distributed unevenly. Assessments vary, but major reserves are concentrated in regions such as Russia, Iran, Qatar, and the United States. Differences in reserve estimates arise from varying geological assessments and reporting standards. Some international agencies identify Russia as holding the largest proven reserves, while others place Iran slightly higher.
The industry has increasingly turned to unconventional gas sources to meet rising demand, spurred by advancements in horizontal drilling and hydraulic fracturing. As these technologies expand, global estimates of recoverable gas continue to evolve.

Contemporary Role and Importance

Natural gas plays a central role in the modern energy economy. It supports power generation, industrial manufacturing, residential heating, and international energy trade. Its adaptability for liquefaction and conversion to liquid fuels has deepened its global reach. At the same time, its contribution to greenhouse gas emissions places it at the centre of debates concerning the transition to low-carbon energy systems.