A barrel is one of several units of volume applied in various contexts; there are dry barrels, fluid barrels (such as the U.K. beer barrel and U.S. beer barrel), oil barrels, and so forth. For historical reasons the volumes of some barrel units are roughly double the volumes of others; volumes in common use range approximately from 100 to 200 litres (22 to 44 imp gal; 26 to 53 US gal). In many connections the term drum is used almost interchangeably with barrel. In other commercial connections, barrel sizes such as beer keg volumes also are standardised in many countries.