Definition: one (1) Barrel of Oil is forty-two (42) US liquid gallons of liquid measuring 158.987294928 liters. This is based on the 1870s wooden barrel used to transport liquids around the world. It is NOT the 55 gallon drum that became a standard during World War II. The 42-US-gallon oil barrel is a unit of measure. However, such wooden barrels are no longer used to transport crude oil -- the industry now uses tankers and pipelines.
The modern day 55-gallon steel drum (known as the 44-gallon drum in Britain and the 200-litre drum elsewhere) resulted from military shipping requirements in World War II, the first war in which trucks, cold rolled steel, stamp or pattern forging machinery and welding were widely available. The drums helped win the Battle of Guadalcanal in the first U.S. offensive in the South Pacific Theater. The U.S. Navy could not maintain control of the seas long enough to offload aviation fuel for U.S. aircraft ashore, so the drums were often transported to the island on fast ships such as destroyers and shoved over the sides (or, time permitting, lowered in cargo nets). Aviation fuel is lighter than seawater, so the drums floated, and Navy Seabees in small craft corralled the drums.
There has been confusion about the true size of a barrel of oil, and some have assumed that the 55 gallon drum had become the standard. NOT TRUE. The real present day measurement is the old 1870s definition: 42 US gallons.
