Step 1 : Introduction to the question "How many gallons of oil does a standard barrel hold?"
...A barrel, cask, or tun is a hollow cylindrical container, traditionally made of wooden staves bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. Barrel.
What is Beral? A barrel is one of several units of volume applied in various contexts; there are dry barrels, fluid barrels (such as the UK beer barrel and US beer barrel), oil barrels and so on.
Step 2 : Answer to the question "How many gallons of oil does a standard barrel hold?"
By the 1860s, the 42-gallon barrel, or tierce, was a common sight on barges floating down the Allegheny River to refineriess in Pittsburgh. The Petroleum Producers Association officially adopted the 42-gallon barrel in 1872. The U.S. Geological Survey and the U.S. Bureau of Mines followed suit in 1882. The barrel's 42-gallon capacity weighs about 300 pounds and produces about 20 gallons of gas, 12 gallons of diesel fuel and 4 gallons of jet fuel when refined. Source: AOGHS.org