Barrel (bbl)

The 42-gallon barrel traces back to the early American oil industry in the 1860s, when Pennsylvania drillers used wooden barrels of that size to transport crude. The unit stuck, and today every major oil contract, production report, and supply statistic uses it. When a country is said to produce "ten million barrels per day," that means ten million times 42 US gallons flowing out of the ground every single day — a large enough figure that it is often shortened further to "10 mb/d." See the commodity units and contracts guide for how units like this shape price quotes.

In market data, prices are almost always quoted as dollars per barrel. Suppose a barrel costs $80 (a hypothetical example): that $80 buys you the right to 42 gallons of crude oil under the terms of the relevant contract. One standard Brent or WTI futures contract covers 1,000 barrels, so a $1 move in the per-barrel price shifts the contract's total value by $1,000.

A frequent point of confusion: a barrel of crude oil does not produce a barrel of gasoline. Refining breaks crude into multiple products — gasoline, diesel, jet fuel, and others — so the output volumes differ from the input. The abbreviation "bbl" (with a double-b) is used specifically for oil barrels to avoid mix-ups with other uses of the word "barrel" in shipping and trade.