U.S. Energy Information Administration, Form EIA-191, Monthly Natural Gas Underground Storage Report Note: Working gas is defined as the quantity of natural gas in the reservoir that is in addition to base gas and is available for withdrawal. It may or may not be completely withdrawn during any particular withdrawal season. With the release of the most recent Natural Gas Monthly , EIA began publishing base gas levels in natural gas storage facilities through the natural gas query system . Base gas plays an important role in underground natural gas storage, serving to maintain cavern or reservoir pressure and keeping natural gas storage facilities operational. Because of the geologic properties of storage facilities, a certain level of pressure is required to maintain reservoir integrity and to withdraw gas for commercial use. […]