Barrel (unit)

Barrel (unit)

A barrel is one of several units of volume, with dry barrels, fluid barrels (UK beer barrel, U.S. beer barrel), oil barrel, etc. The volume of some barrel units is double others, with various volumes in the range of about 100–200 litres (22–44 imp gal; 26–53 US gal).


Dry goods

  • US dry barrel: 7,056 cubic inches (115.6 L) (~3.28 bushel).
    • Defined as length of stave 28+12 in (72 cm), diameter of head 17+18 in (43 cm), distance between heads 26 in (66 cm), circumference of bulge 64 in (1.6 m) outside measurement; representing as nearly as possible 7,056 cubic inches; and the thickness of staves not greater than 410 in (10 mm)[1] ([Ø ≈ 20.37 in/51.7 cm]). Any barrel that is 7,056 cubic inches is recognized as equivalent.
  • US barrel for cranberries 5,826 cubic inches (95.5 L) (~2.71 bushel)
    • Defined as length of stave 28+12 in (72 cm), diameter of head 16+14 in (41 cm), distance between heads 25+14 in (64 cm), circumference of bulge 58+12 in (1.49 m) outside measurement; and the thickness of staves not greater than 410 in (10.16 mm)[1] ([Ø ≈18.62 in/47.3 cm]). No equivalent in cubic inches is given in the statute, but later regulations specify it as 5,826 cubic inches.[2]

Some products have a standard weight or volume that constitutes a barrel:

Fluid barrel

Fluid barrels vary depending on what is being measured and where. For barrels of oil, see the next section.

In the U.K. a beer barrel is 36 imperial gallons (43 US gal; 164 L). In the U.S. most fluid barrels (apart from oil) are 31.5 US gallons (26 imp gal; 119 L) (half a hogshead), but a beer barrel is 31 US gallons (26 imp gal; 117 L).[5][6]

A keg (of beer) is 15.5 gallons.

Oil barrel

  • Oil barrel, (abbreviation bbl): 42 US gallons (34.9723 imp gal; 158.9873 L)[7](but see caveat below regarding conversion to metric units)

The standard oil barrel of 42 US gallons is used in the United States as a measure of crude oil and other petroleum products. Elsewhere, oil is commonly measured in cubic metres (m3) or in tonnes (t), with tonnes more often being used by European oil companies. International companies listed on American stock exchanges tend to express their oil-production volumes in barrels for global reporting purposes, and those listed on European exchanges tend to express their production in tonnes. There can be 6 to 8 barrels of oil in a ton, depending on density. For example: 256 U.S. gallons [6.1 bbl] of heavy distillate per ton, 272 gallons [6.5 bbl] of crude oil per ton, and 333 gallons [7.9 bbl] of gasoline per ton.[8]

The wooden oil barrel of the late 19th century is different from the modern-day 55-gallon steel drum (known as the 45-gallon drum in Britain and the 210/200-litre/kg drum elsewhere). The 42-US-gallon oil barrel is a unit of measure, and is no longer used to transport crude oil, as most petroleum is moved in pipelines or oil tankers.

In the United States, the 42-US-gallon size of barrel as a unit of measure is largely confined to the oil industry, while different sizes of barrel are used in other industries. Nearly all other countries use the metric system. Many oil-producing countries use the American oil barrel.[citation needed]

The measurement originated in the early Pennsylvania oil fields. In the early 1860s, when oil production began, there was no standard container for oil, so oil and petroleum products were stored and transported in barrels of different shapes and sizes. Some of these barrels would originally have been used for other products, such as beer, fish, molasses or turpentine. Both the 42-US-gallon barrels (based on the old English wine measure), the tierce (159 litres) and the 40-US-gallon (151.4-litre) whiskey barrels were used. 45-gallon barrels were also in common use. The 40-gallon whiskey barrel was the most common size used by early oil producers, since they were readily available at the time.[9]

The origins of the 42-gallon oil barrel are obscure, but some historical documents indicate that around 1866, early oil producers in Pennsylvania came to the conclusion that shipping oil in a variety of different containers was causing buyer distrust. They decided they needed a standard unit of measure to convince buyers that they were getting a fair volume for their money. They agreed to base this measure on the more-or-less standard 40-gallon whiskey barrel, but, as an additional way of assuring buyer confidence, they added an additional two gallons to ensure that any measurement errors would always be in the buyer's favor, on the same principle as that underlying the baker's dozen and some other long units of measure.[citation needed] By 1872, the standard oil barrel was firmly established as 42 US gallons.[10]

The abbreviations 1 Mbbl and 1 MMbbl have historically meant one thousand and one million barrels respectively. They are derived from the Latin "mille" meaning "thousand" rather than the Greek "mega". However, this can cause confusion with the SI abbreviation for mega- (and in non-oil industry documentation Mbbl, "megabarrel", can sometimes stand for one million barrels).

The "b" may have been doubled originally to indicate the plural (1 bl, 2 bbl), or possibly it was doubled to eliminate any confusion with bl as a symbol for the bale. Some sources assert that "bbl" originated as a symbol for "blue barrels" delivered by Standard Oil in its early days.

Barrels per day (abbreviated BPD, BOPD, bbl/d, bpd, bd or b/d) is a measurement used to describe the rate of crude-oil production or consumption by an entity. For example, an oil field might produce 100,000 bpd, and a country might consume 1 million bpd.

Note: BPD is not to be confused with BLPD (barrels of liquids per day), which deals with the total liquid recovered, including water, and not only crude oil.[11] BPD is related to BOE (Barrels of Oil Equivalent), a common way of expressing the energy content of hydrocarbon gases in terms of oil, in order to make comparisons.

According to BP Statistical Review 2006:

  • 1 barrel equals 42 US gallons
  • 1 BPD = 42/24/60 = .0292 GPM
  • 1 GPM = 34.29 BPD
  • 1 barrel equals 158.984 Litres
  • The approximate conversion for BPD to tonnes/year is 49.8, so 100,000 BPD equals around 4,980,000 tonnes per year.

Conversion to metric units

Care must be taken when converting an oil barrel (bbl) to other units of volume, such as cubic metres (m3). Because oil changes in volume depending upon its pressure and temperature, and the standard temperatures differ slightly between the American conventional and international metric systems, the volume must be corrected to standard conditions for temperature and pressure if an extremely accurate conversion is required.

Standards bodies such as the American Petroleum Institute (API) have adopted the convention that if oil is measured in oil barrels, it will be at 14.696 psi and 60 °F, whereas if it is measured in cubic metres, it will be at 101.325 kPa and 15 °C (or in some cases 20 °C). The pressures are the same but the temperatures are different — 60 °F is 15.56 °C, 15 °C is 59 °F, and 20 °C is 68 °F. Ignoring the difference between 60 °F and 20 °C may introduce an error of around 0.4%.

The difference in volume depends on the oil's composition, indicated by its density or API gravity. In warming from 15 °C to 60 °F, a heavy oil with API gravity of 20 (932 kg/m3) will increase in volume by 0.039%. A light oil with API gravity of 35 (848 kg/m3) will increase in volume by 0.047%. Empirically derived lookup tables must be used to do very accurate conversions.

However, if all that is needed is to convert a volume in barrels to a volume in cubic metres without compensating for temperature differences, then this is very straightforward.

  • 1 barrel of oil (bbl) is defined as exactly 42 US liquid gallons.
  • 1 US liquid gallon is defined as exactly 231 cubic inches.
  • 1 inch is defined as exactly 0.0254 metres.

Therefore, 1 bbl = (42 x 231 x 0.02543) m3 = 0.158987294928m3 exactly.


Barrel per calendar day

Barrel per calendar day (bc/d or bcd) is a standard petroleum downstream industry measurement of actual refinery throughput, as opposed to designed capacity. BPD is computed by dividing the number of refined barrels of oil processed by the number of days in the year. This is contrasted to Barrel per stream day which is computed by dividing the number of refined barrels of oil by the actual number of days the refinery was running.

Sub units

In terms of production and consumption, it is common to use thousand barrels per day or million barrels per day. These are commonly written as mbd and mmbd respectively taking "m" as the Roman numeral for 1000. It is important not to confuse these with SI prefixes, where kbd and Mbd would mean a thousand and a million barrels per day respectively.


A barrel can technically be used to specify any volume. Since the actual nature of the fluids being measured varies along the stream, sometimes qualifiers are used to clarify what is being specified. In the oil field, it is often important to differentiate between rates of production of fluids, which may be a mix of oil and water, and rates of production of the oil itself. If a well is producing 10mbd of fluids with a 20% water cut, then the well would also be said to be producing 8 thousand barrels of oil a day (mbod).

In other circumstances, it can be important to include gas in production and consumption figures. Normally, gas is measured in standard cubic feet, but when necessary, this volume is converted to a volume of oil of equivalent enthalpy of combustion. Production and consumption using this analogue is stated in barrels of oil equivalent per day (boed).

In the case of water injection wells, it is common to refer to the injectivity rate in barrels of water per day (bwd).

See also


  1. ^ a b 15 USC 234
  2. ^ cranberry barrel
  3. ^ "U.S. Traditional and Commerciavert". 
  4. ^ 15 USC 237
  5. ^ 27 CFR § 25.11.
  6. ^ Ian Whitelaw. A Measure of All Things: The Story of Man and Measurement. Macmillan. p. 60. 
  7. ^ B. N. Taylor. "B.8 Factors for Units Listed Alphabetically - Section B". Guide for the Use of SI units. NIST. Retrieved 2007-10-18. 
  8. ^ "How much, for what, and ending up where?". United Nations Environment Programme Global Marine Oil Pollution Information Gateway. 
  9. ^ Judith O. Etzel (2008). "The 42 Gallon Barrel (History)". The 150th Anniversary of Oil. Oil Region Alliance of Business, Industry and Tourism. Retrieved 2008-04-11. 
  10. ^ "Barrel (of petroleum)". Units and Systems of Units. Sizes, Inc. 2004. Retrieved 2008-04-11. 
  11. ^ Schlumberger Limited. "Schlumberger Oilfield Glossary". Schlumberger Limited. Retrieved 2010-08-27. 

External links

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