Liquefied Natural Gas (LNG) is a cryogenic liquid form of natural gas with most of the heavy components removed (it is predominantly methane with some ethane, propane, and nitrogen). The liquefaction of natural gas allows its transportation over long distances without pipelines, typically using ships, rail, or trucks. The global trade of LNG is expected to double in the next ten years as natural gas exceeds 25% of global energy sources. LNG is used to supplement natural gas distribution systems (which typically rely on pipeline supplies), to generate electrical power, for meeting peak demands, and as engine fuel.
The energy content of LNG varies considerably depending on the composition of the source gas as well as the process used to convert the gas to a liquid. Additionally, the average energy value of a bulk container of LNG changes with time, or ages, since the methane evaporates at a different rate than the other components. These facts in combination with the difficulties associated with any cryogenic fluid (LNG has a boiling point of -162°C) make LNG an unusual and very challenging liquid to measure.