|  Definitions, Sources and Explanatory Notes |
|--------------------------------------------------|
|  Category:   | Natural Gas Storage              |
|-----------------------------|----------------------------------|
|                             |
|  Topic:      | U.S. Underground Storage by Type |
|                         |
|-------------------------|
|   Definitions |  |
|                         |
| Key Terms                 | Definition                                                                                                                                                                                                |
|---------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Base (cushion) 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. |
| Gas in storage            | The sum of base gas plus working gas.                                                                                                                                                                     |
| Injections                | The volume of gas injected into storage reservoirs.                                                                                                                                                       |
| Natural Gas               | A gaseous mixture of hydrocarbon compounds, the primary one being methane.                                                                                                                                |
| Net Withdrawals           | The amount by which storage withdrawals exceed storage injections.                                                                                                                                        |
| Salt Cavern Storage Field | A storage facility that is a cavern hollowed out in either a salt "bed" or "dome" formation.                                                                                                              |
| Withdrawals               | The volume of gas withdrawn from storage reservoirs.                                                                                                                                                      |
| Working (top storage) 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 |
|-----------------|
|  |
|--|
|  | Form EIA-191, "Monthly Underground Gas Storage Report" and Form EIA-176, "Annual Report of Natural and Supplemental Gas Supply and Disposition".  Background on "Natural Gas Monthly" data
- Natural Gas Survey Forms and Instructions       	Explanatory Notes      Gas in storage at the end of a reporting period may not equal the quantity  derived by adding or subtracting net injections or withdrawals during the  period to the quantity of the gas in storage at the beginning of the period.  This is due to changes in the quantities of native gas included in base gas  and/or losses in base gas due to migration from storage reservoirs.  
  Totals may not equal sum of components due to independent rounding.  
  Geographic coverage is the 50 States and the District of Columbia. Prior to January 2013, Alaska data were not included in U.S. totals.  
  Positive net withdrawals indicate the volume of withdrawals in excess of   injections.  Negative net withdrawals indicate the volume of injections in  excess of withdrawals. |