text: are there 55 gallons in a barrel? (oil purposes)? for example, when they quote oil prices they always quote it in barrels. 1 barrel (bbl) of petroleum or related products = 42 gallons or a barrel may be called a "drum", but a drum usually holds 55 gallons...oil has not been shipped in barrels for a very long time since the introduction of oil tanker ships, but the 42-us-gallon size is still used as a unit for measurement, pricing, and in tax and regulatory codes. although some companies still ship some oil in 55-gallon steel drums. (volumes for these are still given in 42-gallon "barrels.")...care must be taken to correct for the effects of temperature, which can cause oil to expand or contract..