Volume of gas which is required in underground storage field to maintain minimum field pressure. This cushion gas (or base gas) is not available for withdrawal so long as the storage site is being actively operated.

The cushion gas is only produced when the facility is decommissioned.

The quantity of natural gas needed to maintain adequate reservoir pressures and deliverability rates throughout the withdrawal season. Base gas is usually not withdrawn and remains in the reservoir. All natural gas native to a depleted reservoir is included in the base gas volume.