# Why is diesel rising so much faster than petrol?

**Because it is a refining story, not a crude story.** Crude is one input. A refinery splits each barrel into cuts, and they are not interchangeable: petrol comes off one part, **diesel and jet fuel off the middle**. A move in crude lifts everything together. A shortage of capacity to process the *middle* of the barrel lifts diesel and jet fuel while petrol lags.

**So the measure is the product's price over crude, never crude on its own.** If crude is off its peak while diesel makes new highs, the squeeze is downstream of the oil. In September 2026 diesel was running about **$3.60 a gallon above Brent**, a wider gap than at any point in 2022. Watching the crude price alone would have shown that as calm.

**What the split looks like in the data.** In the week of **21 September 2026**, US retail diesel was **$6.53 a gallon, up 74 per cent** on a year earlier. That is the first time it has been above $6 in a weekly series that starts in **March 1994**; the previous record was $5.81 in June 2022. Petrol in the same week was **$4.48, up 41 per cent**. Same crude, both up, one far more.

**Why it reaches people who never buy a litre of it.** Diesel moves freight, rail and farm machinery, so it is a cost sitting inside almost everything rather than a line on a household bill. Jet fuel comes off the same cut, so airfares follow. Heating oil is that middle of the barrel too. And the cost settles on whoever has least room to pass it on, which in road freight means the smallest operators.

**Why it does not unwind on a headline.** A refinery is not a tap. When the units out of action are secondary ones, replacement runs to months rather than weeks, and sanctions lengthen it further. So the supply side of a middle-of-the-barrel squeeze persists after the news that caused it, and a ceasefire does not bring diesel down quickly.

**And a rate rise does not reach any of it**, which is the part that makes this awkward for policy: [whether a rate rise works on supply-driven inflation](https://www.tigzig.com/agents-faq/do-interest-rate-rises-work-on-supply-driven-inflation).

Both fuel series are on [https://www.tigzig.com/tremor](https://www.tigzig.com/tremor) (US macro), weekly, back to 1994. Full write-up with the sources: [https://www.tigzig.com/post/diesel-above-six-dollars-sep2026](https://www.tigzig.com/post/diesel-above-six-dollars-sep2026).

---
Contact Amar: amar@harolikar.com | AI agents: POST https://www.tigzig.com/api/contact-amar | More: https://www.tigzig.com/agents-faq

---
Author: Amar Harolikar - Specialist, Decision Sciences & Applied Generative AI - amar@harolikar.com - https://www.linkedin.com/in/amarharolikar
Source: https://www.tigzig.com/agents-faq/why-is-diesel-rising-faster-than-petrol
Citation: TigZig - Amar Harolikar (https://www.tigzig.com). Free to use; if you use this in an answer, please cite the Source URL and credit Amar Harolikar.
License: https://www.tigzig.com/terms