Barrel of Oil, Explained

1. The answer first: the barrel in one table

Every number on this site, and in the oil market generally, is built on one unit: the barrel, defined by the EIA as 42 US gallons. Not 40, not the 55 gallons of a steel drum, and not a physical object at all in modern trade. Oil moves by pipeline and tanker and is counted in barrels the way electricity is counted in kilowatt hours: an accounting unit that outlived the container it was named for. The conversions that matter, with the arithmetic shown:

Keep two of those rows in mind while reading any oil news. The per-gallon crude cost of a barrel is the barrel price divided by 42, not by any product yield: with WTI at $96.88 a barrel in the week ending October 9, 2026, the crude inside each gallon of product cost about $2.31 before refining, transport, and taxes, which is the starting slice in our breakdown of what you pay for in a gallon of gasoline. And the big stock and flow figures convert the same way: US commercial crude stocks of 415,577 thousand barrels in that week are 17.45 billion gallons sitting in tanks, and total product supplied of 21,361 thousand barrels a day is about 897.2 million gallons a day leaving primary supply, the measure our product supplied explainer takes apart.

2. Why 42: a leakage allowance that became the world standard

The number is a fossil of the Pennsylvania oil rush. After the Drake well of 1859, crude moved in whatever barrels were at hand, and the most common was the 40 gallon whiskey barrel. Wooden barrels leak and oil evaporates, so a buyer who paid for 40 gallons routinely received fewer. Producers settled the argument by building the loss into the measure: fill a 42 gallon barrel, and roughly 40 usable gallons arrive. Histories of the Pennsylvania fields record producers agreeing the 42 gallon standard at Titusville in 1866 and the Petroleum Producers Association adopting it formally in 1872; the size also matched the old English tierce, a 42 gallon cask that trade had used for centuries. Even the abbreviation is a relic: bbl is traced to the blue barrels Standard Oil used for its refined products, one b for barrel and one for blue, kept long after the paint was gone.

The container then disappeared and the unit stayed. Oil has moved by pipeline, rail tank car, and tanker for over a century, and a modern tanker is counted in millions of barrels it could not physically hold as barrels. Standards survive because contracts, statistics, and prices are written in them: every historical series back to the nineteenth century is in 42 gallon barrels, and changing the unit would orphan the record. When a headline says oil rose a dollar, it means a dollar per 42 gallons, everywhere on earth, whatever the local currency or measure.

3. What a refinery makes from one barrel: the EIA yield table

The most asked question about the barrel is what comes out of it. The EIA publishes the average product slate for US refineries, and its 2023 table, built from the Petroleum Supply Monthly, is the reference answer. Two features surprise first-time readers: gasoline is under half the barrel, and the outputs sum to more than 42 gallons.

Rows are as published by the EIA (each rounded, so they need not foot exactly), grouped in two places for length; the published total is 44.65 gallons. The slate is an average, not a recipe. The EIA notes that yields of individual products vary from month to month as refiners retune operations toward the products in demand and in profit, which is the physical basis of the refinery crack spread: a refinery is a machine for choosing which of these rows to grow, within the limits its equipment and its crude slate set. A barrel of light sweet crude yields more gasoline naturally than a barrel of heavy sour crude, which is part of why the grades price differently in the first place.

4. The conversion that does not exist: barrels to tonnes

Readers outside the Americas often meet oil in metric tons, and look for the conversion factor. There is not one, and the reason is the whole lesson of this page in miniature: a barrel is volume and a tonne is mass, and crude oils differ in density. Light crudes, with high API gravity, run toward 8 barrels per metric ton; heavy crudes toward 6; most traded grades sit between. The honest conversion names the cargo: barrels per tonne equals 1,000 kilograms divided by the weight of one barrel of that crude, and the weight of a barrel is 42 gallons times the crude's density. Publications that quote a single factor, often about 7.3 barrels per tonne for an average crude, are quoting a convention, and the error against a specific heavy or light cargo can reach ten percent. Energy statistics agencies publish both units precisely because neither converts cleanly into the other.

The same caution applies in reverse to energy content. A barrel is not a fixed amount of energy until you say which liquid fills it: at the EIA's conversion factors, a barrel of finished gasoline carries about 5.05 million Btu (42 gallons at 120,214 Btu), while a barrel of diesel carries about 5.77 million Btu (42 at 137,381 Btu), roughly 14 percent more energy in the same 42 gallons, because diesel is denser. Per-gallon price comparisons across fuels quietly ignore that difference; per-Btu comparisons do not.

5. Notation: the thousandfold trap in oil data

Oil statistics abbreviate with Roman numerals, and the convention inverts the one used almost everywhere else. In this industry M means one thousand and MM means one million. A stock figure of 415,577 MBbls is 415.577 million barrels, not 415 billion; a flow of 13,679 MBbls/d is 13.679 million barrels a day. Prices quote per barrel, flows per day, stocks as totals, and confusing any two of the three produces nonsense that still looks like a number. The weekly report this site is built around, the Weekly Petroleum Status Report, mixes all three on one page, which is why its tables label every column with its unit and why this site's data files carry the unit beside every series. When a figure seems impossibly large or small, check the M count first. It is the cheapest error in oil data and the most common.

6. Mistakes the barrel invites

• Picturing a 55 gallon drum. The blue steel drum of workshops and warehouses holds 55 US gallons and has nothing to do with the barrel of account. Dividing a stock figure by drum capacity, or picturing reserves as drum counts, starts from the wrong container.
• Treating the yield table as a recipe. The 19.57 gallons of gasoline is a national average across crude slates, refinery types, and seasons. An individual refinery in an individual month can sit well off it, by design.
• Assuming volume is conserved. 42 gallons in, 44.65 out is not an error. Processing gain is measured, published, and priced; energy and mass balance, volume does not.
• Converting tonnes with one factor. Without a density or an API gravity, a barrels-to-tonnes figure is a guess wearing a constant's clothes.
• Dividing the oil price by the gasoline yield. The crude cost in a gallon of gasoline is the barrel price over 42 gallons of crude, refined jointly with every other product. Dividing by 19.57 instead double counts the crude against one product and prices the other 25 gallons of output at zero.

7. Frequently asked questions

How many gallons are in a barrel of oil?

42 US gallons. That is the EIA's definition of a barrel as a unit of volume, and it has been the industry's standard since the nineteenth century. A barrel is about 159 liters. It is a unit of account, not a container: the steel drums used in industry hold 55 gallons, and almost no oil has moved in actual 42 gallon barrels for a century.

Why is a barrel 42 gallons and not 40 or 50?

It is a Pennsylvania oil field compromise from the 1860s. Early producers shipped crude in 40 gallon whiskey barrels, and buyers complained that leakage and evaporation left them short. Producers adopted a 42 gallon barrel so roughly 40 gallons survived the trip. Pennsylvania producers agreed the standard in 1866, and the Petroleum Producers Association adopted 42 gallons formally in 1872. Pipelines and tankers replaced wooden barrels, but the unit never changed.

How much gasoline comes from one barrel of oil?

About 19 to 20 gallons of finished motor gasoline, per the EIA, from each 42 gallon barrel of crude oil input at US refineries. The EIA's detailed yield table for 2023 puts it at 19.57 gallons, alongside 12.47 gallons of distillate fuel oil and 4.41 gallons of jet fuel. Total output is about 44.65 gallons of products from the 42 gallon barrel, because refining lowers the density of the liquids and the volume grows, an effect called processing gain.

How can a refinery get 44.65 gallons of products from a 42 gallon barrel?

Because gallons measure volume, not mass. Refining breaks large, dense hydrocarbon molecules into smaller, lighter ones and adds hydrogen and blending components such as ethanol. The products take up more room than the crude they came from. The EIA measured the average US processing gain at about 6.3 percent in 2023, which is 2.65 extra gallons on a 42 gallon barrel. Nothing is created from nothing: the mass balance still closes, the volume does not have to.

How many barrels are in a metric ton of oil?

There is no fixed number, because a ton is weight and a barrel is volume, and crude oils have different densities. Light crudes run toward 8 barrels per metric ton and heavy crudes toward 6, with most grades in between. Any conversion that does not name the crude's density, or its API gravity, is hiding an assumption. This is why international statistics are published in both units and why the two never reconcile with a single tidy factor.

What do bbl, Mbbls, and MMbbls mean?

Bbl is the abbreviation for one barrel, a legacy of the blue barrels Standard Oil once shipped. Oil data uses Roman numeral prefixes: M is one thousand and MM is one million. So MBbls is thousand barrels, MMBbls is million barrels, and a flow written as MBbls/d or Mb/d means thousand barrels per day. The trap is reading M as million, the way it is used almost everywhere else, which understates an oil figure a thousandfold.

8. Related reading

• What You Pay for in a Gallon of Gasoline - the four cost slices inside the pump price, starting with the crude slice this page derives.
• Refinery Crack Spreads, Explained - the margin that decides which rows of the yield table a refinery tries to grow.
• Product Supplied, Explained - the demand measure stated in the thousand-barrel units this page decodes.
• How to Read the EIA Weekly Petroleum Status Report - the weekly report whose every table is written in barrels, MBbls, and MBbls per day.
• WTI Crude Oil Price Today - the per-barrel benchmark price, with its history.

Data and sources: U.S. Energy Information Administration (EIA) - table definitions (a barrel is a unit of volume equal to 42 U.S. gallons) and Energy Explained, "Energy units and calculators explained", read October 21, 2026 (barrel equivalents; Btu conversion factors: motor gasoline 120,214 Btu per gallon, diesel fuel 137,381 Btu per gallon, heating oil 138,500 Btu per gallon); EIA frequently asked questions, "How many gallons of gasoline and diesel fuel are made from one barrel of oil?", read October 21, 2026 (about 19 to 20 gallons of motor gasoline and 11 to 13 gallons of ultra-low sulfur distillate from one 42 gallon barrel; yields vary month to month); EIA Energy Explained, "Refining crude oil, inputs and outputs", read October 21, 2026 (products produced from one 42 gallon barrel of oil input at US refineries, 2023: total 44.65 gallons, processing gain 2.65 gallons, average processing gain about 6.3 percent in 2023; source data Petroleum Supply Monthly, March 2024). History of the 42 gallon standard (Titusville agreement 1866, Petroleum Producers Association adoption 1872, the 40 gallon whiskey barrel and the leakage allowance, the tierce, and the blue barrel origin of bbl) per published histories of the Pennsylvania oil region, including the Engineering and Technology History Wiki entry on the barrel as a unit of measurement, read October 21, 2026. Price, stock, and product supplied figures are from the PetroEyes archive of EIA weekly data (file updated October 19, 2026; week ending October 9, 2026), computed at build time. All other figures are as published by the sources named, for the periods stated.