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Why do We Measure Oil in Barrels?

Michael Pollick
Updated May 17, 2024
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Not every country measures oil in barrels, but that particular measurement is still popular in the United States, which means it remains in the public vernacular even if it has largely lost its significance in a mostly metric world economy. At one point in history, oil producers did store oil in barrels, although the size and nature of those barrels were far from standard.

When the first oil fields were tapped in Pennsylvania during the 1860s, there were no steel 55 gallon drums in which to store the oil. Instead, the oil was pumped into whatever containers could be found, including pickle barrels, cracker barrels and whiskey barrels. There was no standard size oil barrel, but eventually the wooden whiskey barrel became the most popular storage container to hold crude oil until it could be shipped to be refined.

The standard whiskey barrel at the time held approximately 40 gallons of liquid. Early oil producers wanted to ensure their customers received every last drop they ordered, so they actually overfilled the barrels to 42 gallons. This 42 US gallon mark (which is about 35 Imperial gallons and about 160 liters) became the standard measurement of oil in barrels produced in American oil wells.

Eventually the wooden whiskey barrels gave way to steel drums which provided more protection against leakage and contamination. Although these steel drums were designed to hold 55 US gallons of oil, the standard 42 US gallon barrel is still considered to be the correct legal measurement of oil in barrels. When oil producers or economists speak of the number of barrels of oil produced in Saudi Arabia per day, for example, they are applying an American measurement, not one the Saudis themselves might use.

The reason other oil-producing countries rarely use the term "barrels" to measure their production rates is because they rarely store their products in actual barrels anymore. The oil pumped out of the ground is more commonly transported in large tanker trucks or through elaborate pipelines directly to the refineries, or massive cargo ships for overseas delivery.

Individual companies may store oil in barrels, but the largest commercial oil producers rarely do unless the product is going to be shipped to a remote location, such as a military base or third world countries without storage facilities. It is far more likely to see a derivative of crude oil, such as gasoline or kerosene, actually stored in steel drums or barrels.

Therefore, the reason we measure oil in barrels is mostly to provide a familiar reference for those who grew up with images of actual oil-filled barrels rolling down a conveyor belt. In reality, only a percentage of a barrel of oil is converted to gasoline or petrol, so a number such as 1,000,000 barrels of crude oil does not necessarily translate to a surplus supply of gasoline. It only refers to the number of gallons of raw crude produced that day, not how much has been refined into various petroleum products.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Pollick
By Michael Pollick , Writer
As a frequent contributor to About Mechanics, Michael Pollick uses his passion for research and writing to cover a wide range of topics. His curiosity drives him to study subjects in-depth, resulting in informative and engaging articles. Prior to becoming a professional writer, Michael honed his skills as an English tutor, poet, voice-over artist, and DJ.

Discussion Comments

By anon65415 — On Feb 13, 2010

so what is the generally acceptable measurement? --Bussyjoy

By nkbay99 — On Nov 30, 2008

A barrel of oil is 42 gallons. It is a universal unit of measure although I would guess that most oil production companies charge by the ton or metric ton.

No companies store their oil in barrels. That is silly. Oil is stored in oil storage tanks that range in size up to 1,000,000 barrels. (A 1,000,000 tank is about 260 feet in diameter. Oil tanker capacity is measured in tons.

By rleroygordon — On Nov 30, 2008

"cc" means cubic centimeters. It's the volume of the cylinders of an internal combustion or diesel engine when each of the pistons is at its lowest point in the cycle.

By anon22226 — On Nov 30, 2008

There are various sizes of steel drums which could be used to transport oil. The most common barrel is the 55 gallon drum. Sizes vary from about 22 to 24 inches in diameter and 32 to 36 inches in height. The total volume of the barrel is normally greater than the volume of product inside. This is head space which allows for expansion of the product and vapor pressure.

By anon22225 — On Nov 30, 2008

cc stands for cubic centimeter. It is a measure of volume, it is the volume of fluid that can be moved by one stroke of the piston in the cylinder.

By p0506 — On Nov 30, 2008

what do mean by cc, when we say that a particular engine is of xxxx cc.

By anon22221 — On Nov 30, 2008

Why is a US Gallon 1/5th smaller than an imperial Gallon? Why is a 100 pounds called a hundred weight while an imperial hundred weight is 112 lbs. My thought is that there were some thieves among the original colonists or the ships crews. Can you prove me wrong?

By timoleon — On Nov 22, 2008

what is the actual size of an oil barrel?

centimeters or inches pls

Michael Pollick

Michael Pollick


As a frequent contributor to About Mechanics, Michael Pollick uses his passion for research and writing to cover a wide...
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