A commercial unit of volume used to measure liquids such as beer and wine. The official U. S. definition of the barrel is 31.5 gallons, which is about 4.211 cubic feet or 119.24 liters. This unit is the same as the traditional British wine barrel. In Britain the barrel is now defined to be 36 Imperial gallons, which is substantially larger: about 5.780 cubic feet or 163.66 liters. This unit is slightly smaller than the traditional British beer and ale barrel, which held 5.875 cubic feet or 166.36 liters. There are other official barrels, defined in certain U.S. states; most of them fall in the general range of 30-40 gallons. A barrel of beer in the U.S., for example, is usually 31 U.S. gallons (117.35 liters). The origin of the standard symbol bbl is not clear. The "b" may have been doubled originally to indicate the plural (1 bl, 2 bbl), or possibly it was doubled to eliminate any confusion with bl as a symbol for the bale (see above). Note: Some web sites are claiming that "bbl" originated as a symbol for "blue barrels" delivered by Standard Oil in its early days; this is incorrect because there are citations for the symbol at least as early as the late 1700s, long before Standard Oil was founded