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Fueling for Natural Gas Vehicles

CNG Versus Traditional Fuels

Compressed Natural Gas (CNG) saves up to 50% over conventional fuels, and CNG vehicles are available for all types of applications, including business fleets and vehicles for personal use.

CNG is sold at retail stations in Gasoline Gallon Equivalents (GGE) and CNG usage at private stations is also converted to GGE by owners of these stations for fuel cost comparison and tax purposes.

One GGE = 1.25 therms of natural gas (approximately)

Example: If a fleet operator is paying $0.60 per therm to supply natural gas to his CNG fueling equipment then the delivered commodity cost is $0.60 x 1.25 = $0.75/GGE.

Of course, the operator would have to add the cost of amortizing his fueling equipment, maintenance, electricity, etc. so the final cost would likely be something more in the range of $1.50 – 2.00/GGE before taxes.

The commodity cost of natural gas is only about 20% of the total cost of CNG at the pump, so any increases in the commodity price would not have as large an increase at the pump. Since all the other costs components of CNG are relatively constant, this insulates fleets from the effects of any spikes in the price of the underlying commodity. Whereas, since the commodity is about 70% for gasoline/diesel, a sudden spike in oil prices would translate to a correspondingly larger increase at the pump.

The fuel economy of a gasoline vehicle converted to run on CNG is about the same, so you can compare fuel costs on an “apples to apples” basis once you calculate the cost of CNG using the 1.25 therms per GGE conversion above. If you get 25 mpg with gasoline, you would average 25 miles per GGE with natural gas but it would likely cost much less to fill up.

For diesel vehicles being replaced by CNG vehicles, the conversion factor is 1.38 therms per Diesel Gallon Equivalent (DGE). When comparing the two fuels it is important to also note the fuel economy (miles per gallon) of a natural gas spark-ignited engine is slightly less than a diesel cycle engine due to the lower compression ratio of natural gas engines. This difference in fuel economy will be about 5 – 10%, depending on the type of diesel engine being replaced, duty cycle of the vehicle, etc. However, the cost of natural gas per DGE is typically as much as 50% less than diesel so there is more than enough savings to make up for the lower miles per gallon.

Fueling Stations for Natural Gas Vehicles

At CNG stations, the gas is typically taken from the local gas utility’s line at low pressure, compressed and dispensed into the vehicle's storage tanks at high pressure, typically to 3,600 psi. There are two basic types of fueling equipment: fast-fill and time-fill.

Fast-fill systems combine a compressor and a high-pressure storage system. The storage system, called a cascade, fills the vehicle's fuel tank in about the same time it takes to fuel a regular vehicle.
Time-fill systems do not have a storage system and typically compress the gas directly into the vehicle storage cylinders to refuel vehicles while they are parked overnight.
Public CNG stations are currently limited, but the number of locations is expanding rapidly. Individual consumers or public/private fleet operators may also choose to install their own CNG fueling stations.

Use the U.S. Government Department of Energy's Alternative Fueling Station Locator to find the public station nearest you.


Commercial CNG compression, storage and other related fueling equipment is available from many manufacturers. The compression equipment is often custom built to site specifications. However, several equipment manufacturers offer standard packages for small to medium size installations.

Purchasing a FuelMaker Phill
A Vehicle Refueling Appliance (VRA) or Home Refueling Appliance (HRA), known as the "Phill” unit, is available for homes or small businesses.