Liquefied natural gas (sometimes liquid natural gas, frequently LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled to liquid form for ease and safety of non-pressurized storage or transport. It takes up approximately 1/600th the volume of natural gas in the gaseous state at standard temperature and pressure.
LNG is odorless, colorless, non-toxic, and non-corrosive. Hazards include flammability after vaporization into a gaseous state, freezing and asphyxiation. The liquefaction process involves removal of certain components, such as dust, carbon dioxide, helium, water, and heavy hydrocarbons, which could cause process upsets downstream. The natural gas is then condensed into a liquid at close to atmospheric pressure by cooling it to approximately ; maximum transport pressure is set at around , which is approximately 1.25 times atmospheric pressure at sea level. The gas stream is typically separated into the liquefied petroleum fractions (butane and propane) and the lighter ethane and methane fractions. These lighter fractions of methane and ethane make up the bulk of LNG that is liquefied and stored.
Before the late 20th century natural gas was largely considered a byproduct of oil production. The development of production processes, cryogenic storage, and transportation made it possible to commercialize natural gas, creating a global market which now competes with other fuels. The development of LNG storage made natural gas transportation much more reliable. Unlike simple tank storage used for other fuels, natural gas previously could not be stored for extended periods due to the difficulty of preventing gas leakage. Large-scale cryogenic storage made it possible to create reliable long-term storage reserves for natural gas as well. These reserves of liquefied gas could be quickly deployed through regasification processes, and today are the main means for networks to handle local peak shaving requirements.
Production of LNG is an energy intensive process concentrated in a few countries, and typically requires specialized ports for handling the export of the LNG for use in other countries. As of 2023, the United States, Australia and Qatar had the most capacity for exporting LNG, and China, Japan, and South Korea were the biggest importers. A 2025 report by the IEA found that more capacity would be coming on in the upcoming decade. This hyper-concentration of production creates choke points in global supply chains, with the 2026 Iran war affecting Qatar's LNG exports, causing a ripple effect in LNG access and cost.
Specific energy content and energy density The heating value depends on the source of gas that is used and the process that is used to liquefy the gas. The range of heating value can span ±10 to 15 percent. A typical value of the higher heating value of LNG is approximately 50 MJ/kg or 21,500 BTU/lb. A typical value of the lower heating value of LNG is 45 MJ/kg or 19,350 BTU/lb.
For the purpose of comparison of different fuels, the heating value may be expressed in terms of energy per volume, which is known as the energy density expressed in MJ/litre. The density of LNG is roughly 0.41 kg/litre to 0.5 kg/litre, depending on temperature, pressure, and composition, compared to water at 1.0 kg/litre. Using the median value of 0.45 kg/litre, the typical energy density values are 22.5 MJ/litre (based on higher heating value) or 20.3 MJ/litre (based on lower heating value).
The volumetric energy density of LNG is approximately 2.4 times that of compressed natural gas (CNG), which makes it economical to transport natural gas by ship in the form of LNG. The energy density of LNG is comparable to propane and ethanol but is only 60 percent that of diesel and 70 percent that of gasoline.Fuels of the Future for Cars and Trucks, Dr. James J. Eberhardt, U.S. Department of Energy, 2002 Diesel Engine Emissions Reduction (DEER) Workshop, August 25–29, 2002
History By the middle of the seventeenth century Robert Boyle had derived the inverse relationship between the pressure and the volume of gases. About the same time, Guillaume Amontons was investigating the effect of temperature on gases. Early in the nineteenth century Cagniard de la Tour showed there was a temperature above which a gas could not be liquefied. In 1886 Karol Olszewski liquefied methane, the primary constituent of natural gas.
The first large-scale liquefaction of natural gas in the U.S. was in 1918 when the U.S. government liquefied natural gas as a way to extract helium, which is a small component of some natural gas. This helium was intended for use in British dirigibles for World War I. The liquid natural gas (LNG) was not stored, but regasified and immediately put into the gas mains.
Because of large volumes it is not practical to store natural gas, as a gas, near atmospheric pressure. However, when liquefied, it can be stored in a volume 1/600th as large. This is a practical way to store it but the gas must be kept at .
The key patents having to do with natural gas liquefaction date from 1915 and the mid-1930s. In 1915, Godfrey Cabot patented a method for storing liquid gases at very low temperatures. It consisted of a Thermos bottle-type design which included a cold inner tank within an outer tank, the tanks being separated by insulation.
In 1937 Lee Twomey received patents for a process for large-scale liquefaction of natural gas. The intention was to store natural gas as a liquid so it could be used to support peak energy loads during cold snaps. Twomey used a variant of the Linde process. In this process, the gas is cooled regeneratively by continually passing and expanding it through an orifice until it is cooled to temperatures at which it liquefies. This process was developed by James Joule and William Thomson and is known as the Joule–Thomson effect. A variation of the Linde process, called the Claude process, is sometimes used.
The cascade process emerged in the 1960s. Engineers at Phillips Petroleum Company developed the Optimized Cascade Process, which employed three successive refrigeration cycles—propane for precooling, ethylene (or ethane) for intermediate cooling, and methane for final liquefaction. This stepwise approach improved thermodynamic efficiency and operational stability. It was first applied commercially at the Kenai LNG plant in Alaska in 1969, the first baseload LNG export facility in the United States.
Commercial operations in the United States
The East Ohio Gas Company built a full-scale commercial LNG plant in Cleveland, Ohio, in 1940 just after a successful pilot plant built by its sister company, Hope Natural Gas Company of West Virginia. This was the first such plant in the world. Originally it had three spheres, approximately in diameter containing LNG at . Each sphere held the equivalent of about of natural gas. A fourth tank, a cylinder, was added in 1942. It had an equivalent capacity of of gas. The plant operated successfully for three years. The stored gas was regasified and put into the mains when cold snaps hit and extra capacity was needed. This precluded the denial of gas to some customers during a cold snap.
The Cleveland plant failed on October 20, 1944, when the cylindrical tank ruptured, spilling thousands of gallons of LNG over the plant and nearby neighborhood. The gas evaporated and caught fire, which caused 130 fatalities. The fire delayed further implementation of LNG facilities for several years. However, over the next 15 years new research on low-temperature alloys, and better insulation materials, set the stage for a revival of the industry. It restarted in 1959 when a U.S. World War II Liberty ship, the Methane Pioneer, converted to carry LNG, made a delivery of LNG from the U.S. Gulf Coast to energy-starved Great Britain. In June 1964, the world's first purpose-built LNG carrier, the Methane Princess, entered service. Soon after that a large natural gas field was discovered in Algeria. International trade in LNG quickly followed as LNG was shipped to France and Great Britain from the Algerian fields.
The LNG industry in the U.S. restarted in 1965 with the building of a number of new plants, which continued through the 1970s. These plants were not only used for peak-shaving, as in Cleveland, but also for base-load supplies for places that never had natural gas before this. A number of import facilities were built on the East Coast in anticipation of the need to import energy via LNG. However, hydraulic fracturing ("fracking") created a boom in U.S. natural gas production, resulting in import facilities being repurposed as export facilities. The first U.S. LNG export was completed in early 2016.
By 2023, the U.S. had become the biggest exporter in the world, and projects already under construction or permitted would double its export capacities by 2027. The largest exporters were Cheniere Energy Inc., Freeport LNG, and Venture Global LNG Inc. The U.S. Energy Information Administration reported that the U.S. had exported in 2023.
LNG life cycle
The process begins with the pre-treatment of a feedstock of natural gas entering the system to remove impurities such as H2S, CO2, H2O, mercury and higher-chained hydrocarbons. Feedstock gas then enters the liquefaction unit where it is cooled to between −145 °C and −163 °C.World Bank Group. Comparison of Mini-Micro LNG and CNG for Commercialization of Small Volumes of Associated Gas: World Bank; 2015. Although the type or number of heating cycles and/or refrigerants used may vary based on the technology, the basic process involves circulating the gas through aluminum tube coils and exposure to a compressed refrigerant. As the refrigerant is vaporized, the heat transfer causes the gas in the coils to cool. The LNG is then stored in a specialized double-walled insulated tank at atmospheric pressure ready to be transported to its final destination.
Most domestic LNG is transported by land via truck/trailer designed for cryogenic temperatures. Intercontinental LNG transport travels by special tanker ships. LNG transport tanks comprise an internal steel or aluminum compartment and an external carbon or steel compartment with a vacuum system in between to reduce the amount of heat transfer. Once on site, the LNG must be stored in vacuum insulated or flat bottom storage tanks. When ready for distribution, the LNG enters a regasification facility where it is pumped into a vaporizer and heated back into gaseous form. The gas then enters the gas pipeline distribution system and is delivered to the end-user.
The final stage of the LNG life cycle is combustion by the end user, potentially for electricjty generation or other industrial processes. Combustion turns it into carbon dioxide and water which enter the atmosphere. Some methane is lost during this cycle; these leaks into the atmosphere are trapped and constitute a GHG. Methane gas is generally less harmful for human health than coal, but it is a greater contributor to climate change due to leaks and flaring.
Production
The natural gas fed into the LNG plant will be treated to remove water, hydrogen sulfide, carbon dioxide, benzene and other components that will freeze under the low temperatures needed for storage or be destructive to the liquefaction facility. LNG typically contains more than 90% methane. It also contains small amounts of ethane, propane, butane, some heavier alkanes, and nitrogen. The purification process can be designed to give almost 100% methane. One of the risks of LNG is a rapid phase transition explosion (RPT), which occurs when cold LNG comes into contact with water.