A gas holder, or gasometer, is a large container in which natural gas or town gas is stored near atmospheric pressure at ambient temperatures. Town gas is a general term referring to manufactured gaseous fuels produced for sale to consumers and municipalities.

The volume of the container follows the quantity of stored gas, with pressure coming from the weight of a movable cap. Typical volumes for large gas holders are about 50,000 cubic metres (1,800,000 cu ft), with 60 metres (200 ft) diameter structures.

Gas holders now tend to be used for balancing purposes, to ensure gas pipes can be operated within a safe range of pressures, rather than for actually storing gas for later use.

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