L&R Committee 2014 Final Report 

Appendix A – Items: 232-2, 232-3, 237-1, 237-3, and 237-5: GGE of Natural Gas as Vehicular Fuel 

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Appendix A 

Handbook 130 

Uniform Method of Sale and 

Uniform Engine Fuels and Automotive Lubricants Regulation 

Items: 

232-2, 232-3, 237-1, 237-2, 237-3, and 237-5: Background and Justification for Handbook 130 Definition 

of “Diesel Gallon Equivalent (DGE)” of Natural Gas as a Vehicular Fuel 

Clean Vehicle Education Foundation 

Development of the “Gasoline Gallon Equivalent” by NCWM*

In 1993, under the auspices of the National Conference on Weights and Measures 

(NCWM), a Compressed Natural Gas (CNG) Working Group came together to 

determine the way in which CNG would be sold to the public at retail as a motor fuel. . 

The working group focused on three issues: 

1. How to provide the Natural Gas Vehicle (NGV) industry a method of sale that 

would be familiar and acceptable to consumers 

2. How to provide weights and measures officials a verifiable and quantifiable 

means to determine the accuracy of natural gas dispensers; and 

3. How to meet these requirements with a uniform, national standard. 

NCWM considered three proposals for the method of sale of CNG: 

1. joules, the unit of energy measurement in SI units 

2. mass 

3. the Gasoline Gallon Equivalent (GGE) 

The Natural Gas Vehicle Coalition (now NGVAmerica) recommended that the Gasoline 

Gallon Equivalent be adopted as the method of sale for CNG, and that it be based on 

the energy equivalent of a gallon of gasoline. The use of the GGE was recommended 

primarily for the convenience of the retail customer comparing the cost and fuel 

economy of a natural gas vehicle to a comparable gasoline vehicle. During the 

discussion, a proposal was made to eliminate the reference to energy content of CNG 

and replace it with a fixed conversion factor based on mass, with the fixed mass of CNG 

 

* Report of the 78th National Conference on Weights and measures, 1993, NIST Special Publication 854, pp 322-

326. 

Report of the 79th National Conference on Weights and Measures, 1994, NIST Special Publication 870, pp 213-

217. 

Program and Committee Reports for the National Conference on Weights and Measures, 79th Annual Meeting, 

July 17 - 21, 1994, NCWM Publication 16, pp 89-92. 
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being equal to a gallon of gasoline. Measurement of mass in the retail dispenser and 

verification by W&M officials is easier and less costly than measurement of energy 

content. 

Since the energy content of a unit measure of CNG (standard cubic foot - scf) and 

gasoline (gallon) vary widely depending on the sample of fuel measured, the reference 

gallon of gasoline was determined to be Indolene, the gasoline used by EPA to certify 

emissions and fuel economy, with an energy content (lower heating value) of 114,118 

BTU/gal. Work conducted by the Institute of Gas Technology and the Gas Research 

Institute (now combined into the Gas Technology Institute) surveyed 6811 samples of 

natural gas nationwide and concluded that the “average” natural gas in the US had an 

energy content (lower heating value) of 923.7 BTU/scf, and a density of 0.0458172 

lbs/cubic foot. This translates 20,160.551 BTU/lb. Dividing gasoline’s 114.118 BTU/gal 

by natural gas’s 20,160.551 BTU/lb gives 5.660 lbs of natural gas = 1 GGE. Similar 

calculations determined that a gasoline liter equivalent of natural gas equals 0.678 kg of 

natural gas. 

At its 79th annual meeting in July of 1994, NCWM adopted resolutions that:

“All natural gas kept, offered or exposed for sale or sold at retail as a 

vehicle fuel shall be in terms of the gasoline liter equivalent (GLE) or 

gasoline gallon equivalent (GGE), and 

All retail natural gas dispensers shall be labeled with the conversion factor 

in terms of kilograms or pounds. The label shall be permanently and 

conspicuously displayed on the face of the dispenser and shall have either 

the statement “1 Gasoline Liter Equivalent (GLE) is equal to 0.678 kg of 

Natural Gas” or “1 Gasoline Gallon Equivalent (GGE) is equal to 5.660 lbs 

of Natural Gas” according to the method of sale used.” 

These statements can be found in NIST Handbook 130*

, along with the definition of 

“natural gas” which seems to apply only to Compressed Natural Gas, not to Liquefied 

Natural Gas. Handbook 130, §§3.11 and 3.12 (Engine Fuels, Petroleum Products, and 

Automotive Lubricants Regulations) confirm that these requirements are for CNG, rather 

than LNG. Similar requirements and definitions are found in Handbook 44. 

During the discussions it was recognized that, although diesel and gasoline are both 

sold in gallon units, a gallon of diesel fuel has substantially more energy content than a 

gallon of gasoline. While it is convenient to use the Gasoline Gallon Equivalent unit 

when comparing the cost and fuel economy of gasoline-powered light-duty vehicles to 

equivalent natural gas vehicles, a Diesel Gallon Equivalent unit would be more useful 

for operators of medium and heavy-duty (usually diesel powered) vehicles. However, in 

1994, the NCWM working group “agreed to defer development of a “Diesel Gallon 

Equivalent” until the issues related to the ‘Gasoline Gallon Equivalent’ were decided by 

 

*

 “Method of Sale Regulation,” §2.27. 
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Appendix A – Items: 232-2, 232-3, 237-1, 237-3, and 237-5: GGE of Natural Gas as Vehicular Fuel 

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the NCWM and agreed to meet again if additional work is necessary.”** The issue of the 

formal definition a Diesel Gallon Equivalent (DGE) unit has not come before NCWM 

from that time until today, although the DGE is often used in the industry, defined as 

6.31 lbs of natural gas. 

Need for a Definition of a “Diesel Gallon Equivalent” Unit 

Today there are an increasing number of commercial vehicles using natural gas as a 

fuel, to lower emissions and Greenhouse Gases, decrease America’s use of petroleum, 

and lower fuel costs (U.S. DOE Clean Cities Alternative Fuel Price Report for April 2012 

shows in Table 2 ‘Overall Average Fuel Price on Energy-Equivalent Basis’ that diesel is 

priced at $4.12/gal and CNG at $2.32/gal 

http://www.afdc.energy.gov/afdc/pdfs/afpr_apr_12.pdf ). 

Since the NCWM’s working group deferred development of a DGE unit in 1994, there 

has been little call by the natural gas vehicle industry for the formalization of that unit in 

the sale of Compressed Natural Gas. However the use of Liquefied Natural Gas 

(LNG) as a motor fuel has been growing and there is significant interest in using the 

DGE as a unit for the sale of that fuel. 

LNG as a motor fuel is used almost exclusively by commercial vehicles, most of which 

view diesel as the conventional alternative. Using the same logic as was used for the 

development of the GGE unit, the convenience of the retail customer comparing the 

cost and fuel economy of a natural gas vehicle to a comparable conventional vehicle, it 

makes sense for NCWM to now “officially” define the DGE. 

Other than §3.12. Liquefied Natural Gas, in the Engine Fuels and Automotive Lubricants 

Regulation section of Handbook 130, we find no specific provisions in either Handbook 

44 or Handbook 130 for the retail sale of LNG as a motor fuel. However LNG is sold in 

California and other states on a mass basis (by the pound), which allows for easy 

confirmation by weights and measures authorities. An “official” definition of the DGE as 

a specific mass of natural gas would allow states to easily move from retail sale by 

pound to retail sale by DGE, simplifying the sale process for the retail customer used to 

dealing with “gallons of diesel” as a fuel measure. 

Therefore, at this time we are asking for a definition of the Diesel Gallon Equivalent (and 

Diesel Liter Equivalent) units by NCWM. 

Justification of the Definition of a DGE as 6.312 Pounds of Natural Gas 

Handbook 130 contains the following definitions of natural Gas as a vehicle fuel*: 

Gasoline liter equivalent (GLE). – Gasoline liter equivalent (GLE) means 

 

** Report of the 79th National Conference on Weights and Measures, 1994, NIST Special Publication 870, p 214 *

 NIST handbook 130, 2006, Method of State Regulation, §§2.27.1.2. and 2.227.1.3.; also Engine Fuels, Petroleum 

Products, and Automotive Lubricants Regulation, §§1.25. and 1.26. 
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Appendix A – Items: 232-2, 232-3, 237-1, 237-3, and 237-5: GGE of Natural Gas as Vehicular Fuel 

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 0.678 kg of natural gas. 

Gasoline gallon equivalent (GGE). – Gasoline gallon equivalent (GGE) means 

 2.567 kg (5.660 lb) of natural gas. 

As the NCWM working group recognized during its deliberations in 1993 on the 

Gasoline Gallon Equivalent unit, both gasoline and natural gas can vary in their BTU 

content from sample to sample. The working group determined the gasoline gallon 

(energy) equivalent based on a gallon of Indolene (114,118 BTU/gal – lower heating 

value) and a survey of 6811 natural gas samples nationwide with an average of 

923.7 BTU/scf (lower heating value) and a density of 0.0458172 lbs/cubic foot. This 

equates to 20,160.551 BTU/lb. Dividing gasoline’s 114.118 BTU/gal by natural gas’s 

20,160.551 BTU/lb gives 5.660 lbs of natural gas = 1 GGE. Similar calculations 

determined that a gasoline liter equivalent of natural gas equals 0.678 kg of natural gas. 

Starting with 5.660 lbs of natural gas = 1 GGE and 0.678 kg of natural gas = 1 GLE, we 

can calculate the mass of natural gas necessary to make a DGE and a DLE by 

comparing the amount of energy in a gallon of diesel fuel to the amount of energy in a 

gallon of gasoline fuel and apply that ratio to scale up the masses of natural gas 

calculated for the GGE and GLE units. 

Unfortunately it is no easier today than it was in 1993 to set one energy value as 

representative of a unit for all gasoline, (or diesel) fuel. EPA’s certification fuel has likely 

changed in energy content since 1993, as both gasoline and diesel fuels have been 

modified for improved emissions. 

We recommend using the most recent Department of Energy Transportation Energy 

Data Book*

, as an authoritative reference for both gasoline and diesel fuel energy 

values. Taking further surveys or basing our calculations on today’s EPA certification 

fuel only delays our action, substantially increases costs, and, in the end, provides a 

limited potential increase in accuracy based on one point in time. Table B.4 of the 

Transportation Energy Data Book, on the heat content of fuels 

http://cta.ornl.gov/data/tedb30/Edition30_Full_Doc.pdf lists the net energy of gasoline as 

115,400 BTU/Gal, and diesel as 128,700 BTU/Gal. 

Therefore a Diesel Gallon Equivalent of natural gas is: 

(128,700/115,400) X 5.660 = 6.312 lb (2.863 kg) 

and a Diesel Liter Equivalent of natural gas is: 

(128,700/115,400 X 0.678 = 0.756 kg 

 

Prepared by: 

Clean Vehicle Education Foundation 

http://www.cleanvehicle.org

 

*

 Stacy C. Davis and Susan W. Diegel, Oak Ridge National Laboratory, Transportation Energy Data Book, 

Edition 30, 2011, ORNL-6978, or http://cta.ornl.gov/data/index.shtml