|  Definitions, Sources and Explanatory Notes |
|--------------------------------------------------|
|  Category:   | Natural Gas Production |
|-----------------------------|------------------------|
|                             |
|  Topic:      | Supplemental Supplies  |
|                         |
|-------------------------|
|   Definitions |  |
|                         |
| Key Terms                           | Definition                                                                                                                                                                                                                                                                                                          |
|-------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Biomass Gas                         | A medium Btu gas containing methane andcarbon dioxide, resulting from the action of microorganismson organic materials such as a landfill.                                                                                                                                                                        |
| Blast-furnace Gas                   | The waste combustible gas generated in a blast furnace when iron ore is being reduced with coke to metallic iron. It is commonly used as a fuel within steel works.                                                                                                                                                |
| British Thermal Unit (Btu)          | The quantity of heat required to raise the temperature of 1 pound of liquid water by 1 degree Fahrenheit at the temperature at which water has its greatest density (approximately 39 degrees Fahrenheit).                                                                                                          |
| Coke-oven Gas                       | The mixture of permanent gases producedby the carbonization of coal in a coke oven at temperatures inexcess of 1,000 degrees Celsius.                                                                                                                                                                             |
| Manufactured Gas                    | A gas obtained by destructive distillationof coal, or by the thermal decomposition of oil, or by the reactionof steam passing through a bed of heated coal or coke. Examplesare coal gases, coke oven gases, producer gas, blast furnace gas,blue (water) gas, carbureted water gas. Btu content varieswidely. |
| Propane-air                         | A mixture of propane and air resulting in a gaseousfuel suitable for pipeline distribution.                                                                                                                                                                                                                        |
| Refinery Gas                        | Noncondensate gas collected inpetroleum refineries.                                                                                                                                                                                                                                                                |
| Supplemental Gaseous Fuels Supplies | Synthetic naturalgas, propane-air, coke oven gas, refinery gas, biomass gas, airinjected for Btu stabilization, and manufactured gas commingledand distributed with natural gas.                                                                                                                                 |
| Synthetic Natural Gas (SNG)         | (Also referred to as substitute natural gas) A manufactured product, chemically similar in most respects to natural gas, resulting from the conversion or reforming of hydrocarbons that may easily be substituted for or interchanged with pipeline-quality natural gas.                                           |
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| For definitions of related energy terms, refer to the   EIA Energy Glossary. |
|  	Sources |
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|  |
|--|
|  | Form EIA-176, "Annual Report of Natural and Supplemental Gas Supply and Disposition".Background on "Natural Gas Annual" data
- Natural Gas Survey Forms and Instructions       	Explanatory Notes         Annual data on nonhydrocarbon gases removed from marketed production-carbon dioxide, helium, 	 hydrogen sulfide, and nitrogen are reported by state agencies on the voluntary 	 Form EIA-895A.   
    Annual data are published from Form EIA-176.  
     All monthly data are considered preliminary until after the publication of the 	 Natural Gas Annual	for the year in which the report month falls. Monthly estimates are 	 based on the annual ratio of supplemental gaseous fuels to the sum of dry gas production, 	 net imports, and net withdrawals from storage. This ratio is applied to the monthly sum of 	 these three elements to compute a monthly supplemental gaseous fuels figure.  
     Monthly data are revised after publication of the Natural Gas Annual. 	 Final monthly data are estimated based on the revised annual ratio of supplemental gaseous 	 fuels to the sum of dry gas production, net imports, and net withdrawals from storage. 	 This ratio is applied to the revised monthly sum of these three elements to compute final 	 monthly data. |