In 1994, the US National Institute of Standards and Technology (NIST) defined "gasoline gallon equivalent (GGE) means 5.660 pounds of natural gas." Compressed natural gas (CNG), for example, is a gas rather than a liquid. It can be measured by its volume in standard cubic feet (ft³) (volume at atmospheric conditions), by its weight in pounds (lb) or by its energy content in joules (J) or British thermal units (BTU) or kilowatt-hours (kW·h). It is difficult to compare the cost of gasoline with other fuels if they are sold in different units. GGE solves this. One GGE of CNG and one GGE of electricity have exactly the same energy content as one gallon of gasoline. CNG sold at filling stations in the US is priced in dollars per GGE.