The lazy question about a record diesel price is what it does to inflation. An index tells you the price moved, never whose margin moved with it. The question worth asking is whether the barrel got dearer or the refining of it did, because only one of those pays a refiner.
AAA's national diesel average printed $6.0556 a gallon on 11 September, the first above $6 and 63.4% above the $3.7053 of a year earlier. The two federal releases put the same move in different places: diesel sits in the producer index, where it jumped 24.1% in August and, in the BLS's own words, accounts for "over a third of the August increase in the index for final demand goods". Gasoline is the consumer-index line, up 3.9% and "over one third of the monthly all items increase". Household heating oil, the CPI's distillate line, rose 10.1% in the month and 52.0% over the year.
Crude fell 1% since June while Gulf Coast diesel rose 25%
Cushing WTI averaged $84.81 in June and $83.90 in August — down 1.1%. Across the same two months Gulf Coast ultra-low-sulphur diesel went from $3.357 a gallon to $4.208, up 25.4%. The table above takes the spread the way a refiner does, at 42 gallons to the barrel minus the crude. August's diesel at $4.208 a gallon is $4.208 × 42 = $176.74 a barrel; $176.74 − $83.90 = $92.84, which is 54% above the 2026 Q2 average of $60.12, and the 9 September spot pair — diesel $4.832, WTI $97.26 — puts it at $105.68, 3.5 times the $29.94 that the third quarter of 2025 averaged. None of that came from the barrel. It came from the spread between the barrel and what leaves the refinery.
Chevron's U.S. Downstream has no volume left to add
Chevron ran 1,070 MBD of crude unit input through its five U.S. refineries in the June quarter at more than 97% utilisation — a record, and the reason our Chevron model says of that line, in its own words, that "throughput is disclosed and is close to its ceiling, so this line is a price and margin story with almost no volume headroom left". The implied nameplate of 1,103 MBD is ours, derived from the disclosed throughput and utilisation, and it leaves 33 MBD to add.
With volume fixed, everything depends on price, and the model drifts price down 7.5% a quarter from $247.41 per input barrel — $18.56 a barrel in the first projected quarter alone.
Exxon has disclosed what a dollar of margin is worth
Energy Products carried 77.6% of Exxon's consolidated revenue in the same quarter, and Exxon publishes the sensitivity that matters: $800m of annual earnings for every $1 a barrel of indicative refining margin. That margin was $29.0 in the basis quarter against $17.5 to $18.3 in the third and fourth quarters of 2025.
Model inputs as of 27 August against the companies' June-quarter disclosures
| Input | What it carries |
|---|---|
| Chevron U.S. Downstream price | $247.41 an input barrel |
| Its quarterly price drift | -7.5%, or $18.56 |
| Exxon Energy Products price | $173.53 a barrel sold |
| Its quarterly price drift | -11.0%, or $19.09 |
| Exxon's disclosed sensitivity | $800m a year per $1/bbl |
| Margin reversion encoded | $29.0 to $17.5-$18.3 |
| What that reversion removes | $8.6bn-$9.2bn a year |
The two prices, the two drifts and the encoded reversion are R40 model assumptions from data built on 27 August, not company guidance; the drifts apply to a deseasonalised revenue-per-barrel input rather than to a refining margin, which is why the dollar amounts beside them are per-barrel revenue and not per-barrel profit. Disclosed by the companies for the June quarter: Chevron's 1,070 MBD of crude unit input at more than 97% utilisation, Exxon's 77.6% revenue share and 5,698 kbd of product sales, the $800m of annual earnings per $1 a barrel of indicative refining margin, the $29.0 basis-quarter margin and the $17.5-$18.3 of 3Q25 and 4Q25. The last row is the $29.0 reversion multiplied by the disclosed sensitivity: $10.7 to $11.5 a barrel at $800m each.
Our Exxon model encodes the journey back. Returning $29.0 to the 2025 range is $10.7 to $11.5 a barrel: $11.5 × $800m = $9.2bn at one end and $10.7 × $800m = $8.6bn at the other, annualised — the reversion the 11% quarterly price drift exists to express. Chevron's drift is gentler and its arithmetic runs the same way.
Both models were built on 27 August, against a basis quarter in which Chevron earned $12.1bn and Brent had already risen 53%. Reversion after a windfall is the conservative assumption, and usually the right one. August ran the other way, and September so far has run further.
What would settle this, and what would not
A pump price is not a refining margin. Neither is our crack: it is one product against one crude, while an indicative refining margin is a whole product slate against the barrels each refinery actually runs, after operating cost, turnarounds and hedges. The two move together and are not the same number, so nothing here converts one into the other — the crack is evidence about direction, not a measurement of either company's margin.
What settles it is the indicative refining margin each company discloses with its third-quarter results at the end of October. Two months of that quarter are already on the tape at cracks well above the basis quarter, and a refiner's realised margin can still land below spot through turnarounds, feedstock cost and hedging.
If the disclosed margin comes in above the basis quarter's $29.0 rather than reverting toward $17.5, the downward drift both models carry is wrong in sign for at least one quarter. At Exxon's own sensitivity, each dollar of that error is $800m a year.
The diesel and gasoline averages, with their year-ago comparisons, are AAA's of 11 September; AAA attributes the move to tighter global supply and refining capacity, an attribution neither company has made. The producer and consumer index changes and the quoted sentences are the Bureau of Labor Statistics' August PPI and CPI releases of 10 and 11 September. Spot diesel and crude are the Energy Information Administration's published series; the crack built from them is ours, not a refiner's margin. Throughput, revenue share, the $29.0 and 2025 margins and the $800m per dollar are the companies' own disclosures for the June quarter. Every drift, ceiling, deseasonalised price and reversion figure is from our models and is an assumption, not a forecast either company has given.
