What is the unit called the petroleum barrel?

men and barrels

Shipping oil in barrels in the early days of the Pennsylvania oil fields.

Detail from Oil Regions of Pennsylvania, #2800, Shipping Oil–Story Farm.
Rochester, NY: Union View Co., no date.

The barrel of petroleum, 1866 – present, a unit of capacity = 42 U.S. gallons (or about 5.61458 cubic feet, and though approximately 158.987 liters is taken as = 159 liters, by, for example, the U.S. Census Bureau Harmonized System), measured at a temperature of 60° Fahrenheit.¹ It is a unit of account; actual barrels containing 42 gallons of crude oil have not been used for more than a century, if ever. For its abbreviations, please see here.

A metric ton of average crude oil at standard temperature and pressure has a volume of about 7.33 barrels. A cubic meter of oil is about 6.29 barrels.

The barrel of petroleum originated in the Pennsylvania oil rush following Drake's discovery well (1859). Its exact origins are somewhat obscure.

The forty-two (wine or U.S.) gallon barrel, one-sixth of the 252-gallon tun, was a well-known size long before Drake's well. It is the size of the English tierce of wine prior to 1824, and of the American cran of herrings.

The earliest documentation from the oil fields,² however, speaks mostly of 40-gallon barrels, not 42, and the report (February 1866) of a federal commission appointed to look into taxing oil gave all its statistics in 40-gallon barrels.³ In 1872,⁴ the government required distillers of alcohol to report their production in 40-gallon barrels.

The oil producers were desperate for containers and would have used any liquid-tight barrel they could lay their hands on. Records and photographs show barrels in a variety of sizes. Where did they get so many 40-gallon barrels that it became a temporary standard?

The 40-gallon barrel had a long history in the state of Virginia. An act of 23 February, 1631-32, ordained that a barrel of corn should contain 5 bushels Winchester measure, which is 40 gallons.⁵ A Virginia act of 18 February, 1819 declared that a barrel of salt contained 5 bushels (or 40 wine gallons; the U.S. gallon is based on the English wine gallon).

Virginia had strong ties with southwestern Pennsylvania. It was there that George Washington did his surveying and land claiming as a youth, and there he personally suppressed the Whiskey Rebellion as President. Until West Virginia broke away in 1863, Virginia lay to the west and south of that corner of Pennsylvania.

One may speculate that a Virginian 40-gallon barrel, either as a standard or the barrels themselves, made it to western Pennsylvania and thus to the oil fields. The original purpose of the barrels may have been to contain whiskey. The main reason the 18ᵗʰ century western Pennsylvanian farmers converted grain to whiskey was to find an economic means of transporting grain over the Alleghenies to market, and there would have been an early and ready market for whiskey barrels. Another possibility lies in the salt connection, as salt was produced by drilling wells for brine. More research is needed on salt, whiskey and cooperage in Pennsylvania, but certainly whiskey barrels would have made excellent containers for crude oil.

The Register says the oil producers have issued the following circular: Whereas, It is conceded by all producers of crude petroleum on Oil Creek that the present system of selling oil by the barrel, without regard to the size, is injurious to the oil trade, alike to the buyer and seller, as buyers with an ordinary size barrel cannot compete with those with large ones. We, therefore, mutually agree and bind ourselves that from this date we will sell no crude by the barrel or package, but by the gallon only. An allowance of two gallons will be made on the gauge of each and every 40 gallons in favor of the buyer.⁶

The probable origin of the 42-gallon petroleum barrel is that in 1866 the producers added an extra 2 gallons to a 40-gallon barrel when they switched to selling by the gallon. (When the basis on which a commodity is measured changes, it is not uncommon for sellers to give buyers a bit extra to allay the buyers' apprehensions, and sometimes these allowances become frozen into the value of a unit. Compare the addition of an extra 4 pounds to each 100 when London began to enforce exact weight in 1256. See sack.) Notice that even at its origin the petroleum barrel was a unit of account. By 1872, the 42-gallon barrel seems to have become firmly established:

At a session of the Council of Producers, the following resolution was passed: “Whereas, False reports have been circulating in the eastern markets to the effect that the producers intend starting their wells again at once; Resolved, ... that we will have $5 per bbl. of 42 gallons for our crude oil.”⁷

The size may have been influenced by the existing standard for barrels of lamp oil produced by the meat packers in Cincinnati, Ohio. Those barrels contained 43 gallons, according to Alexander (1850).

2. For example,
Thomas A. Gale.
The Wonder of the Nineteenth Century; Rock Oil in Pennsylvania and Elsewhere.
Erie, PA: Sloan and Griffeth, 1860. [back]

4. R.S. 3308, (a1872). Authorized barrel of proof spirits.— Every distiller shall make a return of the number of barrels of spirits distilled by him, counting forty gallons of proof spirits to the barrel, whenever such return is demanded by the collector of the district. [back]

6. Derrick's Hand Book of Petroleum. Volume 1.
Oil City, PA: Derrick Publishing Company, 1898. [back]

Robert Etter Hardwicke.
The Oilman's Barrel.
Norman, Oklahoma: University of Oklahoma Press, 1958.

Well-researched standard work and about as conclusive as the evidence permitted. See especially his critique of the Van Syckle theory, advanced in the Oil and Gas Journal, 15 April 1921.

barrel (of petroleum)