What a barrel of crude becomes

42 gallons in. About 44.4 gallons out.

This is not an error. Cracking breaks large molecules into smaller ones, and smaller molecules take up more room, so a refinery returns more volume than it receives. The EIA reports it as a line item called processing gain, and at the foot of the diagram you can see it: the red bar runs past the black one.

Below is every major step between the two, drawn as descent. Crude at the top, one ancestor. The first split is the only purely physical one in the whole process; everything after it is chemistry. At the bottom, lines rejoin, because the gasoline in your tank has at least four separate lineages.

How to read it

Red means measured. Every red figure is an EIA refinery yield. Nothing inferred or drawn for structure is ever red.

Width means volume, and only at the two ends. No line in the middle carries a quantity, because no intermediate quantity is published. Drawing one would be a guess wearing the costume of a measurement.

Dashed red is hydrogen. It runs backwards up the diagram: the reformer makes the hydrogen that cleans its own feed. Refining is not a tree, and that loop is why.

Line weight is charge capacity, and the figure under a unit is that capacity as a share of crude distillation. These are a different kind of number from the yields: capacity is what a unit is built to process, not what it processed. Potential, not actual.

How much each lane can process

Unit	Capacity	Share of crude
Catalytic hydrotreating, distillate	6,268,465 b/sd	32.7%
Catalytic cracking, fresh feed	5,334,708	27.8%
Catalytic hydrotreating, naphtha / reformer feed	4,490,487	23.4%
Catalytic reforming	3,549,453	18.5%
Coking, delayed and fluid	2,793,645	14.6%
Catalytic hydrocracking, gas oil	1,468,600	7.7%
Visbreaking	16,000	0.1%

Those come to 124.8% of crude distillation capacity. It is the second thing in this diagram that looks like an error and is not. It exceeds 100% because a barrel's components are processed more than once: gas oil is cracked, and the product is hydrotreated again before it is blended. The barrel gets bigger, and it gets handled more times than there is barrel.

What these units actually do

Cracking, coking, reforming. The names are trade words, but there are only four things any of them can do to a molecule: cut it up, stick it together, change its shape, or take the sulfur out. Everything in the diagram is one of those.

Separating

No chemistry at all. Heat the crude and the lighter molecules boil off first, so the barrel sorts itself by boiling point. Everything after this step changes the molecules.

Atmospheric distillation 100% of the barrel: Splits by boiling point. The first and last purely physical split.
Vacuum distillation: Re-boils the atmospheric residue under vacuum, below its cracking temperature.

Breaking

Big molecules into small ones. The heavy end of a barrel is worth little and there is a lot of it, so refineries break it apart. This is where the extra volume comes from: two small molecules take up more room than the one big molecule they came from.

Fluid catalytic cracker 28% of the barrel: Breaks gas oil into lighter molecules. Where most of the extra volume comes from.
Coker 15% of the barrel: Cracks the vacuum residue until what is left is solid carbon.
Hydrocracker 8% of the barrel: Cracks under hydrogen. Favours jet and diesel over gasoline.

Rearranging

Same molecule, different shape. Octane is not about size but about how a molecule is built, so these units take a low-octane stream and fold it into a high-octane one without making it any bigger.

Catalytic reformer 18% of the barrel: Rearranges heavy naphtha into aromatics. Makes the hydrogen the hydrotreaters need.
Isomerization 4% of the barrel: Rearranges light naphtha into higher-octane shapes. Same size, better structure.

Joining

Small molecules into bigger ones. The gases left over from cracking are too light to put in a tank, so they are stitched together into something that belongs in gasoline.

Alkylation 7% of the barrel: Runs the other way: joins small molecules into larger, high-octane ones.

Cleaning

Taking the sulfur out. Crude carries sulfur, sulfur becomes acid rain and poisons catalysts, and the limits are legal ones. Hydrogen pulls it out as hydrogen sulfide.

Distillate hydrotreater 33% of the barrel: The unit that made ultra-low-sulfur diesel possible.
Naphtha hydrotreater 23% of the barrel: Runs before the reformer, not after: sulfur poisons the reforming catalyst.
Desalter: Washes out salt and water before heat.
Kerosene hydrotreater: Sulfur out, on spec for jet.

What is absent

The visbreaker: US visbreaking capacity is 16,000 barrels a day against 2,793,645 for coking. These yields are American, so a unit at 0.08% of the barrel is left out rather than drawn at a scale it does not have. In Europe and Asia it would belong.
Miscellaneous products, 0.5%: EIA's residual category. No single lineage produces it, so it is named rather than given a parent it does not have.
Actual throughput: Capacity is published; what ran through it in a given month is not, at this level of detail. So the lanes carry what they could process rather than what they did. An earlier version of this page said no per-unit figure existed at all, which was wrong.
Where the plastic is: Only 1.3% of the barrel is labelled petrochemical feedstock here, and that is not how much oil becomes plastic. EIA names a product for what it is, not where it goes, so the hydrocarbon gas liquids and still gas that feed crackers are counted as themselves. Most US plastics feedstock is ethane from shale gas, which never passes through a refinery and so cannot appear in a refinery yield at all. Petrochemicals take about 16% of global oil demand. None of that is answerable from this diagram, because the destination is not in the source. It needs its own.

Sources

U.S. Refinery Yield: Every percentage on this page. July 2026, as percent of crude oil input.
EPA AP-42 ch. 5.1, Petroleum Refining: Which unit feeds which. Derivation only; it publishes no volumes.
EIA Refinery Capacity Report, data as of 2026-01-01: Capacity by unit type, as of 1 January 2026. The basis for leaving the visbreaker out.
EIA, refinery downstream charge capacity by unit: Downstream charge capacity, per unit. What each lane can process.
IEA, Oil 2025: Petrochemical feedstock as a share of global oil demand. The basis for saying this diagram cannot answer where the plastic is.