|  Definitions, Sources and Explanatory Notes |
|--------------------------------------------------|
|  Category:   | Natural Gas Storage                       |
|-----------------------------|-------------------------------------------|
|                             |
|  Topic:      | Weekly Working Gas in Underground Storage |
|                         |
|-------------------------|
|   Definitions |  |
|                         |
| Key Terms               | Definition                                                                                                                                                                                                                                                                                                                             |
|-------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Base Gas                | The volume of gas needed as a permanent inventory to maintain adequate reservoirpressures and deliverability rates throughout the withdrawal season. All native gas is included in the base gas volume.                                                                                                                              |
| East Region             | Connecticut, Delaware, District of Columbia, Florida, Georgia, Iowa, Illinois, Indiana, Kentucky, Massachusetts, Maryland, Maine, Michigan, Missouri, North Carolina, Nebraska, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, Wisconsin, and West Virginia. |
| Natural Gas             | A gaseous mixture of hydrocarbon compounds, the primary one being methane.                                                                                                                                                                                                                                                             |
| Producing Region        | Alabama, Arkansas, Kansas, Louisiana, Mississippi, New Mexico, Oklahoma, and Texas.                                                                                                                                                                                                                                                    |
| Underground Gas Storage | The use of sub-surfacefacilities for storing gas that has been transferred from its originallocation. The facilities are usually hollowed-out saltdomes, natural geological reservoirs (depleted oil or gasfields) or water-bearing sands topped by an impermeable caprock (aquifer).                                             |
| West Region             | Arizona, California, Colorado, Idaho, Minnesota, Montana, Nevada, North Dakota, Oregon, South Dakota, Washington, Wyoming, and Utah.                                                                                                                                                                                                  |
| Working Gas             | The volume of total natural gas storage capacity that contains natural gas available for withdrawal.                                                                                                                                                                                                                                   |
|                                                                               |
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| For definitions of related energy terms, refer to the   EIA Energy Glossary. |
|  	Sources |
|-----------------|
|  |
|--|
|  | Week ending Dec. 31, 1993: Form EIA-191, "Monthly Underground Gas Storage Report".
Weeks January 7, 1994 through February 22, 2002:ESTIMATES derived from a computation process that uses both EIA monthly survey data and American Gas Association weekly survey data.
Week ending March 8, 2002: linearly interpolated between the derived weekly estimates that end March 1 and the initial estimate from the EIA-912 on March 15.
Weeks beginning with March 15, 2002: Form EIA-912, "Weekly Underground Natural Gas Storage Report"  
- Natural Gas Survey Forms and Instructions       	Explanatory Notes      This table tracks U.S. natural gas inventories held in underground storage   facilities. The weekly stocks generally are the volumes of working gas as of the   report date. Changes in reported stock levels reflect all events affecting   working gas in storage, including injections, withdrawals, and   reclassifications between base and working gas.  
  The weekly storage estimates are based on a survey sample that does not include   all companies that operate underground storage facilities. The sample was   selected from the list of storage operators to achieve a target standard   error of the estimate of working gas in storage which was no greater than   5 percent for each region. For an expanded discussion of the relationship between the   current and prior estimates, see     Differences Between Monthly and Weekly Working Gas in Storage.  
  This data with supporting charts and analysis can be found in the  Weekly Natural Gas Storage Report.  
The Basics of Underground Natural Gas Storage.  
  Complete documentation of EIA's estimation methodology is available in the   report, Methodology for EIA Weekly Underground Natural Gas Storage Estimates.  
  In October 2003, EIA updated the estimation methodology for the Weekly Natural Gas Storage Report and revised the weekly data back to July 2003 at that time.  As a result, a portion of the net change between 6/27/03 and 7/4/03, 142 billion cubic feet, is attributable to the change in methodologies. |