Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport.

It takes up about 1/600th the volume of natural gas in the gaseous state (at standard conditions for temperature and pressure).

It is odourless, colourless, non-toxic and non-corrosive.

The feed gas generally undergoes pre-treatment involving removal of certain components, such as acid gases, water, and heavy hydrocarbons, which would cause difficulty in the liquefaction process.

The natural gas is then condensed into a liquid at close to atmospheric pressure by cooling it to approximately −162 °C (−260 °F); maximum transport pressure is set at around 25 kPa (4 psi).

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.

Although the type or number of heating cycles and/or refrigerants used may vary based on the technology, the basic process involves passing the gas through aluminium heat exchangers (cold box) and exposure to a compressed refrigerant. As the refrigerant is vaporised, the heat transfer causes the gas in the passes to cool.

The LNG is then stored in a specialised insulated tank at atmospheric pressure ready to be transported to its final destination.