Gasoline gallon equivalent (GGE) or gasolineequivalent gallon (GEG) is the amount of alternative fuel it takes to equal the energy content of one liquid gallon of gasoline. In 1994, the U.S. National Institute of Standards and Technology or NIST defined "Gasoline gallon equivalent (GGE) means 5.660 pounds of natural gas."^{[1]}
GGE allows consumers to compare the energy content of competing fuels against a commonly known fuel  gasoline. Compressed Natural Gas (CNG) for example, is a gas rather than a liquid. It can be measured by its volume in cubic feet (CF), by its weight in pounds (LB) or by its energy content (BTU) or kilowatthours (kWh) It is difficult to compare the cost of gasoline with other fuels if they are sold in different units. GGE solves this. A GGE of CNG and a GGE of electricity all have the same energy content as one gallon of gasoline. CNG sold at filling stations is priced in dollars per GGE.
Contents 
Fuel  Gallon Gasoline Equivalent  BTUs/Unit 

Gasoline (base)^{[2]}  1 US gallon  114,000 BTU/gallon 
Gasoline (conventional, summer)^{[2]}  0.996 US gallon *  114,500 BTU/gallon 
Gasoline (conventional, winter)^{[2]}  1.013 US gallon *  112,500 BTU/gallon 
Gasoline (reformulated gasoline, ethanol)^{[2]}  1.019 US gallon *  111,836 BTU/gallon 
Gasoline (reformulated gasoline, ETBE)^{[2]}  1.019 US gallon *  111,811 BTU/gallon 
Gasoline (reformulated gasoline, MTBE)^{[2]}  1.020 US gallon *  111,745 BTU/gallon 
Gasoline (10% MBTE)^{[3]}  1.02 US gallon  112,000 BTU/gallon 
Gasoline (regular unleaded)^{[4]}  1 US gallon  114,100 BTU/gallon 
Diesel #2^{[4]}  0.88 US gallons  129,500 BTU/gallon 
Biodiesel (B100)^{[4]}  0.96 US gallons  118,300 BTU/gallon 
Bio Diesel (B20)^{[4]}  0.90 US gallons  127,250 BTU/gallon 
Liquid natural gas (LNG)^{[4]}  1.52 US gallons  75,000 BTU/gallon 
Compressed natural gas (CNG)^{[4]}  126.67 cu. ft (3.58 m3)  900 BTU/cu. ft 
Hydrogen at Atmospheric Pressure  357.37 cu. ft  319 BTU/cu. ft^{[5]} 
Hydrogen by weight  1.004 kilograms (2.21 lb) *^{[6]}  119.9MJ/kg (51,532 Btu/lb)^{[7]} 
Liquefied petroleum gas (LPG)^{[4]}  1.35 US gallons  84,300 BTU/gallon 
Methanol fuel (M100)^{[4]}  2.01 US gallons  56,800 BTU/gallon 
Ethanol fuel (E100)^{[4]}  1.500 US gallons  76,100 BTU/gallon 
Ethanol (E85)^{[4]}  1.39 US gallons  81,800 BTU/gallon 
Jet fuel (naphtha)^{[8]}  0.97 US gallons  118,700 BTU/gal 
Jet fuel (kerosene)^{[8]}  0.90 US gallons  128,100 BTU/gal 
Electricity  33.40 Kilowatt hours *  3,413 BTU/kWh ^{[9]}^{[10]} 
*calculated based on 114,000 BTU/gallon base gasoline
One GGE of natural gas is 126.67 cubic feet (3.58 m^{3}). This volume of natural gas has the same energy content as one US gallon of gasoline (based on lower heating values: 900 BTU/CF of natural gas and 115,000 BTU/gallon of gasoline).^{[11]}
One GGE of CNG pressurized at 2,400 psi is 0.77 cubic feet. This volume of CNG at 2,400 psi has the same energy content as one US gallon of gasoline (based on lower heating values: 148,144 BTU/CF of CNG and 115,000 BTU/gallon of gasoline.^{[11]} Using Boyle's Law, the equivalent GGE at 3,600 psi is 0.51 cubic feet which corresponds to 14.5 liters or 3.82 actual US gallons.
The National Conference of Weights & Measurements (NCWM) has developed a standard unit of measurement for compressed natural gas, defined in the NIST Handbook 44 Appendix D as follows: "1 Gasoline [US] gallon equivalent (GGE) means 2.567 kg (5.660 lb) of natural gas."^{[12]}
When consumers refuel their CNG vehicles in the USA, the CNG is usually measured and sold in GGE units. This is fairly helpful as a comparison to gallons of gasoline.
One GGE of ethanol is 1.5 gallons. This volume of ethanol has the same energy content as one US gallon of gasoline. This is because a gallon of ethanol has a lower heat value or energy content (76,100 BTU) when compared to a gallon of gasoline (114,100 BTU).
Ordinary consumers driving a "flexfuel" vehicle can expect a substantial drop in fuel mileage when using 85% ethanol products (the compression ratio is fixed mechanically, and electronic sensors can only modify the timing of the spark and allow the electronic fuel injectors to provide more of the reduced BTU value fuel).
