The actual amount of gas in a pipeline or distribution system. The placing daily gas imbalance (unsold gas) into a cumulative imbalance for sale at a later time. As gas is transported along a pipeline, its pressure falls due to friction in the pipe, and also as gas is taken off at various points. To compensate, compressor stations are built at strategic points, which lift the pressure back up. This helps transport larger amounts than would otherwise be possible. At times of low demand, this pressure can be raised, and then allowed to fall gradually during high demand, when the flow is greater. This is called “linepack storage”, and is utilized mainly within the higher pressure pipelines used to transmit gas throughout the country.

A 50-mile (80 km)section of 42-inch transmission line operating at about 1,000 pounds of pressure contains about 200 million cubic feet of gas