Liquefied Natural Gas (LNG)

What Is Liquefied Natural Gas?

Liquefied natural gas (LNG) (also called cryogenic natural gas or super-cooled methane) is natural gas, composed predominantly of methane (CH₄), that has been purified and cooled to approximately -162 degrees Celsius (-260 degrees Fahrenheit) at atmospheric pressure, reducing its volume to roughly 1/600th of its gaseous state. This dramatic volume reduction makes it economical to store and transport by sea in specially designed cryogenic tankers, connecting gas-producing regions such as Qatar, Australia, and the United States Gulf Coast to import-dependent markets in Asia and Europe that cannot be served by pipeline.

Key Takeaways

LNG is natural gas cooled to -162 degrees Celsius, shrinking its volume to 1/600th of the gaseous state and enabling ocean transport.
The liquefaction process uses multi-stage refrigeration cycles; the APCI propane pre-cooled mixed refrigerant (C3-MR) cycle dominates global capacity.
LNG trains, the modular processing units at export terminals, typically produce 3 to 8 million tonnes per annum (MTPA) each.
Regasification terminals receive LNG, warm it back to gas, and inject it into domestic pipeline networks at the destination market.
Global LNG trade reached approximately 400 million tonnes per year (MT/y) in 2024, with Asia-Pacific accounting for more than 65 percent of imports.

How Liquefied Natural Gas Works

Raw natural gas arriving at an LNG export terminal first undergoes pre-treatment to remove impurities that would freeze solid or damage equipment at cryogenic temperatures. Acid gases (CO₂ and H₂S) are stripped in amine contactor columns, water is removed by molecular sieve beds, mercury is captured on sulfur-impregnated activated carbon, and heavy hydrocarbons are separated in a scrub column. The treated, sales-quality gas then enters the liquefaction train.

The dominant commercial liquefaction technology is the Air Products and Chemicals Inc. (APCI) propane pre-cooled mixed refrigerant process, universally referred to as the C3-MR cycle. In this cycle, propane refrigerant first cools the gas stream from ambient temperature to approximately -35 degrees Celsius in a series of kettle-type heat exchangers. The pre-cooled gas then enters the main cryogenic heat exchanger (MCHE), a coil-wound unit sometimes called the "cold box," where a proprietary mixed refrigerant blend of nitrogen, methane, ethane, and propane chills the stream to the final -162 degrees Celsius liquefaction point. An alternative technology, ConocoPhillips Optimized Cascade, uses pure-component propane, ethylene, and methane refrigerant circuits in series and is the basis for all LNG trains at Sabine Pass, Corpus Christi, and Freeport in the United States.

Once liquefied, LNG is stored in large double-wall, full-containment tanks on-site at the export terminal, typically holding 160,000 to 200,000 cubic metres each, before loading onto LNG carriers for ocean transport. At the destination, regasification terminals receive the cryogenic liquid into similar storage tanks, then pass it through open-rack or submerged combustion vaporizers that warm the LNG back to ambient-temperature gas, which is metered and injected into the domestic transmission pipeline grid.

Fast Facts: Liquefied Natural Gas

Boiling point: -162 degrees Celsius (-260 degrees Fahrenheit) at atmospheric pressure
Volume ratio: 1 volume LNG equals approximately 600 volumes of natural gas at standard conditions
Density: approximately 430 kg/m³ (roughly half the density of water)
Typical LNG train capacity: 3 to 8 MTPA per train
Carrier capacity: 125,000 to 266,000 m³ (Q-Max vessels reach 266,000 m³)
Global trade volume (2024): approximately 400 MT/y
Top exporters (2024): Australia, Qatar, United States
Top importers (2024): China, Japan, South Korea, European Union

Field Tip:

Boil-off gas (BOG) continuously evaporates from LNG storage at roughly 0.05 to 0.15 percent of tank volume per day even with excellent insulation. LNG carriers and terminal operators must manage BOG carefully: reliquefaction compressors recondense it, it can be used as fuel for the vessel's propulsion system, or it can be vented to a flare stack as a last resort. A carrier burning BOG as fuel rather than heavy fuel oil (HFO) reduces voyage fuel costs and emissions simultaneously.

LNG Carrier Types and Trade Routes

LNG carriers fall into two main hull-tank designs. Membrane carriers use thin stainless-steel or Invar alloy membranes bonded to the ship's inner hull as the primary containment barrier, with insulating foam panels between the membrane and the hull structure. GTT Mark III and No. 96 are the leading membrane systems and account for the majority of new-build orders. Moss-type carriers use self-supporting spherical aluminum tanks mounted above the ship's deck, giving them their distinctive ball-tank silhouette. Moss vessels are more robust against sloshing damage but have less cargo-to-ship-size efficiency than modern membrane designs. Qatar's Q-Flex (210,000 m³) and Q-Max (266,000 m³) supercarriers use membrane containment and are the largest LNG vessels afloat, built specifically for the Qatari mega-trains at Ras Laffan.

Principal long-haul trade routes run from Qatar and Australia to Japan, China, and South Korea across the Pacific, and from Qatar and the United States to Europe via the Atlantic basin. U.S. Gulf Coast exports, which ramped up sharply after 2016 through the Sabine Pass terminal and expanded further at Corpus Christi, Freeport, Cameron, and Sabine Pass Train 6, have restructured global LNG pricing by introducing large volumes of hub-priced, destination-flexible cargoes. Unlike traditional LNG contracts, which indexed the price to crude oil (typically at a slope of 11 to 15 percent of Japan Crude Cocktail, or JCC), U.S. contracts are often tied to Henry Hub natural gas futures plus a liquefaction tolling fee, allowing buyers to arbitrage between Atlantic and Pacific basin markets.

cryogenic LNG -- used in engineering and safety contexts to emphasize the extremely low storage temperature
super-cooled methane -- a general-audience description highlighting the cooling process
LNG cargo -- a specific shipment of LNG on a tanker, measured in standard cubic metres or British thermal units
LNG train -- one modular liquefaction processing unit at an export terminal, with a defined nameplate capacity in MTPA

Frequently Asked Questions About Liquefied Natural Gas

Is LNG the same as compressed natural gas (CNG)?

No. LNG is liquefied by cooling to -162 degrees Celsius at near-atmospheric pressure; its liquid state makes it highly dense and suitable for long ocean voyages. Compressed natural gas (CNG) remains in its gaseous state and is stored at high pressure, typically 200 to 250 bar, in steel cylinders. CNG is practical for short-range vehicle fuel and pipeline balancing but cannot economically be shipped across oceans. The two technologies serve different markets and use entirely different infrastructure.

How is LNG priced, and what is the difference between oil-indexed and hub-priced LNG?

Historically, LNG contracts sold into Asia were priced as a percentage of the Japan Crude Cocktail (JCC) oil price, typically at a slope of 13 to 15 percent with an S-curve that flattens at very high or very low oil prices. This oil-indexed pricing arose because Asian buyers initially viewed LNG as an oil substitute for power generation. U.S. LNG exports introduced hub-priced contracts pegged to Henry Hub (the benchmark U.S. natural gas price), plus a fixed liquefaction tolling fee of roughly $2.25 to $3.50 per million British thermal units (MMBtu). European hub-priced LNG often references Title Transfer Facility (TTF) in the Netherlands. As global LNG supply grows, more contracts are shifting toward gas-on-gas competition pricing rather than oil indexation.

What happens if an LNG tanker is involved in an accident?

LNG is not explosive in its liquid state. If spilled on water, it vaporizes rapidly into a cold methane vapor cloud. Ignition requires the vapor concentration to be between approximately 5 and 15 percent in air (the flammable range of methane). Below 5 percent, it disperses harmlessly; above 15 percent, it is too rich to ignite. LNG carriers are built to International Maritime Organization (IMO) IGC Code standards with double-hull construction and multiple safety barriers. The historical safety record of ocean LNG transport is exceptionally strong; no LNG carrier has experienced a cargo-related fatality at sea in over 50 years of commercial trade.

Why Liquefied Natural Gas Matters in Oil and Gas

LNG has transformed natural gas from a regional commodity constrained by pipeline geography into a globally traded, fungible energy product. Countries without domestic gas resources or overland pipeline access, including Japan, South Korea, Taiwan, and much of South and Southeast Asia, depend entirely on LNG imports for gas-fired power generation and industrial feedstock. For producers, LNG monetizes stranded gas reserves that would otherwise be uneconomic, and the capital scale of export projects, often $10 billion to $50 billion per terminal, creates decades-long anchor contracts that underpin national energy strategies. As governments in Europe and Asia accelerate coal-to-gas switching as a lower-carbon bridging fuel, and as global LNG capacity continues to grow through projects in the United States, Qatar, Mozambique, and Canada, LNG is central to both near-term energy security and the longer-term trajectory of the global energy transition.