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 $107.17 a barrel in the week ending October 23, 2026, the crude inside each gallon of product cost about $2.55 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 410,625 thousand barrels in that week are 17.25 billion gallons sitting in tanks, and total product supplied of 20,209 thousand barrels a day is about 848.8 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.

Worked example: scaling the yield table to a day of refining

The yield table is per barrel, but refinery data is reported as a daily flow, so the useful move is to scale it. Take an illustrative input of 16.0 million barrels of crude a day, a round number in the range US refiners run in a busy month (the live figure is in the weekly report). Each product's daily output is the input times its gallons per barrel, divided by 42:

Two lessons come out of the arithmetic. First, the products leaving the refinery gate exceed the crude entering it by about a million barrels a day at this scale, so a balance sheet that subtracts product output from crude input to find "losses" will find a negative number every time. That is processing gain, not an accounting error. Second, a refinery that pushes its gasoline yield up by one gallon per barrel, from 19.57 to 20.57, adds about 0.38 million barrels a day of gasoline on the same 16.0 million barrels of crude (16.0 times 1 divided by 42). Small changes in the yield slate move product balances as much as changes in crude runs do, which is why seasonal shifts between gasoline and distillate output show up in weekly stocks before any change in refinery utilization.

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.

Doing the conversion properly: from API gravity to barrels per tonne

The industry describes a crude's density with API gravity, and the EIA glossary gives the defining formula: degrees API equals 141.5 divided by the specific gravity at 60 degrees Fahrenheit, minus 131.5. Turn it around and specific gravity is 141.5 divided by (API plus 131.5). A barrel is 0.158987 cubic meters (42 US gallons of 3.785 liters), and water at 60 degrees Fahrenheit weighs about 999 kilograms per cubic meter, so the mass of one barrel is 0.158987 times the specific gravity times 999 kilograms, and barrels per metric ton is 1,000 divided by that mass. Worked through for a range of gravities:

The table shows why a single factor misleads. Apply a generic 7.3 barrels per tonne to a 20 degree heavy cargo and the barrel count comes out about 8 percent too high (7.3 against 6.74); apply it to a 40 degree light cargo and it comes out about 4 percent too low (7.3 against 7.63). On a 100,000 tonne cargo of the heavy grade, that is 730,000 barrels claimed against 674,000 actually loaded, a difference of 56,000 barrels. The fix is mechanical: ask for the API gravity on the assay or bill of lading, run the three steps above, and the tonne and the barrel describe the same oil.

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. The same factors give a quick bridge to natural gas, which the EIA puts at 1,036 Btu per cubic foot: matching the energy in one barrel of diesel takes about 5,570 cubic feet of gas (5.77 million divided by 1,036), and one barrel of gasoline about 4,870 cubic feet. Any "barrel of oil equivalent" figure for gas rests on a conversion of this kind, and it is worth checking which factor the publisher used before comparing two companies' reported production.

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.
• Mixing cubic meters and barrels without the factor. Several national statistics offices report oil in cubic meters. One cubic meter is about 6.29 barrels, so a field producing 10,000 cubic meters a day is producing roughly 62,900 barrels a day, not 10,000.
• Ignoring the reference temperature. The API gravity definition fixes specific gravity at 60 degrees Fahrenheit because oil expands as it warms. Volumes measured warm and quoted without correction overstate the oil in a tank, which is why measurement for sale is corrected to that standard temperature.

7. Thirty-three years of the barrel: how the slate has moved

The 2023 yield table in section 3 is the one the EIA's explainer still shows, and it was last updated in June 2024. The agency's annual refinery yield series runs further, to 2025, and back to 1993, and it answers a question a single year cannot: is the barrel changing? Read the series end to end and the answer is yes, but not in the row most people would guess. Gasoline, the product the barrel is usually pictured as making, has barely moved. Everything around it has.

Gasoline's share of refinery input never left a band of 44.2 to 47.8 percent in the whole period: the low was 2008 and the high was 2021. In 2025 it was 45.9 percent, which is 19.28 gallons per 42 gallon barrel, a little below the 2023 figure of 19.57 gallons quoted above and almost exactly the 19.36 gallons of 1993. Distillate fuel oil, the diesel and heating oil row, is the one that moved. It was 21.9 percent of the barrel in 1993, 9.20 gallons, and 30.0 percent in 2025, 12.60 gallons. The ratio of gasoline to distillate output fell from 2.11 to 1.53 over the period. Residual fuel oil, the heavy bottom of the barrel, went the other way, from 5.8 percent to 1.9, or from 2.44 gallons to 0.80. Over three decades the heavy end of the US barrel shrank and the middle grew, and the series shows it without needing to name a single refinery project.

The heavy end did not simply disappear, and the smaller rows of the same series show where some of it went. Petroleum coke, which the EIA's glossary describes as a residue high in carbon and low in hydrogen left by cracking, rose from 4.3 percent of the barrel in 1993 to 5.4 percent in 2011 to 2013 and again in 2016, before easing to 4.6 percent in 2025. Asphalt and road oil fell from 3.2 percent to 2.0 over the full period. Put the two middle-distillate rows together and the shift is plainer still: distillate fuel oil and kerosene-type jet fuel were 31.1 percent of the barrel in 1993 and 41.0 percent in 2025, almost ten points more of every barrel going to diesel, heating oil and jet fuel. That is the long-run backdrop to the diesel price guide: the yield series is the simplest public record of how much more of each barrel now goes to the fuels that guide covers.

Two years in the series are worth reading closely because they show the slate responding to demand within a year rather than over decades. In 2020, when air travel collapsed, the jet fuel yield fell to 6.9 percent, its lowest in the series, from 10.5 in 2019, and the distillate yield rose to 32.0, its highest. The yield data record the shift, not how each plant made it, but the two rows moved in opposite directions in the same year. By 2024 the jet yield had recovered to 11.0 percent, and it held there in 2025: the highest jet share in the series. That is the flexibility the yield table in section 3 hints at when it calls the slate an average and not a recipe, measured in a single year.

Processing gain, the extra volume that makes 42 gallons in become more than 42 out, also moves. The EIA's explainer gives about 6.3 percent for 2023; the annual series shows 5.9 percent in both 2024 and 2025, against a range of 5.3 percent (1994 and 1995) to 6.9 percent (2010 and 2011). At 5.9 percent a 42 gallon barrel of input comes out as about 44.5 gallons of products, rather than the 44.65 of the 2023 table. The difference looks small, but on the illustrative 16.0 million barrels a day of crude in section 3, 0.4 percentage points of gain is about 64 thousand barrels a day of product that is not there. When a source quotes the yield table, check the year; the series revises its picture of the barrel every twelve months.

8. Barrels of oil equivalent: a 6-to-1 rule that is about energy, not money

The barrel is also borrowed as a unit for things that are not oil. Oil and gas producers report their output and reserves in barrels of oil equivalent, written boe, so that a company producing both can give one number. A common convention converts natural gas at six thousand cubic feet (6 Mcf) to one barrel. Murphy Oil's 2025 annual report on Form 10-K is one example: it states its production "on a barrel of oil equivalent basis (six thousand cubic feet of natural gas equals one barrel of oil)" and labels the conversion "an energy equivalent basis of 6:1."

The EIA's heat content tables let you test that rounding. In 2025 the agency puts US crude oil production at 5.689 million Btu per barrel and dry natural gas at 1,036 Btu per cubic foot, which makes the energy in one barrel of crude equal to the energy in about 5.49 thousand cubic feet of gas. The industry's 6 is close to that, rounded up. The same tables put imported crude at 6.062 million Btu per barrel and exported crude at 5.716, a gap of about 6 percent. A barrel is a volume, so the energy in it depends on what fills it, the same lesson section 4 draws for mass.

The energy match is not a value match, and that is where boe figures mislead. Divide the annual average WTI spot price by the annual average Henry Hub price, both from the EIA, and you get the number of million Btu of gas that one barrel of crude would buy:

Sources: EIA annual Cushing WTI spot price (RWTC) and Henry Hub natural gas spot price (RNGWHHD); EIA Monthly Energy Review, Table A4, dry natural gas 1,036 Btu per cubic foot (2025). Ratios and values are PetroEyes arithmetic; 6 Mcf is 6.216 million Btu at that heat content.

Six Mcf of gas, the quantity that counts as one barrel in a boe total, was worth between 17.8 and 42.2 percent of a barrel of WTI in these five years, and 33.5 percent in 2025. In none of the five years did it reach half. A worked example shows what that does to a reported number. Take a hypothetical producer reporting 100,000 boe a day, split evenly: 50,000 barrels of oil and 300,000 Mcf of gas. At the 2025 benchmark averages the oil earns about $3.27 million a day and the gas about $1.09 million, so gas is half of the boe figure but 25.1 percent of the revenue, and the whole stream averages about $43.64 per boe, a third below the WTI price. Real realized prices differ from the benchmarks, and natural gas liquids, which many producers report separately, sit between the two, but the direction holds. Two producers with the same boe output and different oil weightings are not the same size in any sense that matters to revenue. When a boe figure appears in company or government data, the first question is the oil share; the US oil reserves guide and the Henry Hub explainer cover the two halves of that question. This is a reading guide to disclosures, not an assessment of any company.

9. Frequently asked questions

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. Checked October 22, 2026: the EIA glossary entry for API gravity (degrees API equals 141.5 divided by specific gravity at 60 degrees Fahrenheit, minus 131.5) and EIA Energy Explained, units and calculators (natural gas 1,036 Btu per cubic foot; gasoline, diesel, and heating oil factors as above). The barrels-per-tonne table and the 16.0 million barrel refining example are PetroEyes arithmetic on those published factors, with illustrative inputs stated in the text. Price, stock, and product supplied figures are from the PetroEyes archive of EIA weekly data (file updated October 22, 2026; week ending October 23, 2026), computed at build time. All other figures are as published by the sources named, for the periods stated. Checked October 28, 2026 for sections 7 and 8: EIA, U.S. refinery yield, annual (1993 to 2025); EIA Energy Explained, refining crude oil, inputs and outputs (last updated June 20, 2024); EIA Monthly Energy Review, Table A2, heat content of petroleum production, imports and exports (2025); EIA Monthly Energy Review, Table A4, heat content of natural gas (2025); EIA annual WTI spot price; EIA annual Henry Hub spot price; Murphy Oil Corporation, Form 10-K for 2025 (filed February 25, 2026); EIA Monthly Energy Review glossary (petroleum coke). The gallon conversions, ratios and the 100,000 boe a day example are PetroEyes arithmetic on those figures.