Diesel costing more than petrol cannot be explained by oil prices alone: in October 2026, diesel is around €2.33 to €2.35 per litre in France, roughly 20 cents more than petrol, while Brent has fallen back to around $100. The main bottleneck lies between crude oil and the pump: diesel refining margins have soared, while excise duty remains fixed and VAT is still added.

To understand why diesel is more expensive than petrol, the most useful approach is to break down a litre like an invoice. On 12 October 2026, the European Union Oil Bulletin gives a price of €2.328: €1.332 covers the product and its supply chain, €0.608 excise duty and €0.388 VAT. In other words, crude prices can fall without the full decrease reaching the pump.

What do you really pay for in a litre of diesel?

Of the €2.328 per litre recorded on 12 October, the EU Oil Bulletin attributes 57.2%—€1.332—to the product: this includes crude oil, refining, transport and the distributor's margin. Taxes account for €0.996, or 42.8% of the final price: €0.608 excise duty and €0.388 VAT.

The detail matters because these components do not react in the same way. Excise duty is a fixed amount of about 61 cents per litre in 2026: it does not fall when oil prices fall. VAT is proportional to the price and also applies to excise duty. This is why the tax share can even decline as a percentage when fuel becomes more expensive, without the state collecting less in absolute terms.

A 50-litre fill-up at €2.328 therefore costs about €116.40, including €49.78 in taxes under the same European breakdown. This calculation suggests a useful reflex: when you hear that “oil is falling”, check how much of each litre actually depends on crude and how much depends on refining, logistics and taxation.

Why doesn't a lower oil price make diesel cheaper?

The decisive factor is the refining margin, often called the crack spread: the difference between the value of refined diesel and the crude oil needed to produce it. According to data cited by The Conversation, this margin is normally around $20 per barrel. In early September 2026, it exceeded $100 in Europe for the first time.

The Banque de France provides a particularly telling estimate: between February and August 2026, the rise in the crack spread may explain about 15 points of an approximately 26% increase in petroleum products, or nearly 60% of the change. This helps explain October's paradox: diesel can remain very expensive even as Brent falls.

The effect is much stronger for diesel than for petrol. In Northwest Europe, the diesel crack spread averaged around $50 per barrel from April to June, then exceeded $70 in July. For petrol, it was negative in April, then reached $23 in May, $26 in June and $40 in July.

Why is diesel structurally under pressure in Europe?

Diesel is not used only by private cars. In France, it still accounted for 67% of road-fuel consumption in 2025. In 2026, according to Alternatives Économiques, 91% of the six million light commercial vehicles, 92% of coaches and 96% of heavy trucks run on diesel. This professional demand reacts little to a rise of a few cents: a truck or farm machine cannot instantly switch energy source because the price rises.

This rigidity meets weakened supply. The closure of the Strait of Hormuz since the start of the Middle East conflict and Ukrainian strikes on Russian refineries have reduced the availability of refined products. The International Energy Agency, cited in the available data, estimates that refineries processed about 810 million fewer barrels between March and August 2026 than a year earlier, equivalent to 4.4 million barrels per day.

Europe is particularly exposed because its diesel demand exceeds local production capacity. This is fundamentally different from the simplistic idea that cheaper crude oil would be enough: having crude does not mean immediately having the required volume of refined diesel.

The result can be seen across almost the entire Union. In the week of 12 October 2026, diesel averaged €2.080 per litre in the EU-27, versus €1.941 for petrol. Diesel was more expensive than petrol in 24 of 27 countries, with an average gap of about 14 cents.

Should you keep your diesel car or change powertrain?

It would be tempting to give a magic number: “above X kilometres per year, keep diesel; below that, switch to hybrid or electric.” That would be misleading. Available data can tell us fuel prices precisely, but not comparable vehicle consumption, purchase prices, depreciation, maintenance, charging costs or insurance differences. A serious mileage threshold therefore cannot be calculated from these figures alone.

A simple method can be used instead. For each vehicle considered, first calculate its energy cost per kilometre: real-world consumption multiplied by the price per litre, then divided by 100 for a combustion engine. For an EV, use the same principle with consumption in kWh/100 km and your actual kWh price. Then multiply by your annual mileage.

Finally add the cost of changing: purchase-price difference, resale value of your current car, maintenance and other costs that genuinely differ between the two options. Break-even comes when accumulated annual savings offset this extra cost. It is less spectacular than a universal figure, but far more useful: two drivers covering 15,000 km a year can reach opposite conclusions depending on their vehicle and charging method.

An example of deciding without inventing figures

• Keep diesel: compare the cost of changing cars with the annual saving you realistically expect. A temporary rise in diesel prices alone is not enough to justify a major expense.
• Switch to petrol: SP95-E10 was €2.124 versus €2.330 for diesel from 5 to 11 October 2026. But the pump-price gap must be compared with the real consumption of both vehicles.
• Choose a hybrid: the calculation requires its real consumption in your use and its extra purchase cost. Without those two values, quoting a break-even mileage would be artificial.
• Switch to electric: you need the vehicle price, its consumption and, above all, the rate you actually pay for charging. Without these data, no honest per-kilometre comparison is possible.

My practical rule would therefore be not to sell a diesel car solely because a litre costs twenty cents more today. The right indicator is not the large price displayed on the station sign, but the total cost of changing relative to the kilometres you will actually drive. Fuel prices are visible every day; the cost of replacing a car too early is much less obvious.

Frequently asked questions

Why is diesel more expensive than petrol even though oil prices have fallen?

Because crude oil is only one component of a litre. In 2026, diesel refining margins tightened sharply: they exceeded $100 per barrel in Europe in early September, versus about $20 in normal times, which can offset part of the fall in Brent.

What share of the diesel price is tax?

According to the EU Oil Bulletin on 12 October 2026, a litre at €2.328 includes €0.996 in taxes, or 42.8%: €0.608 excise duty and €0.388 VAT. The remaining €1.332 covers the product, refining, transport and distribution margin.

At what annual mileage should you stop using diesel?

There is no universal threshold that can be calculated from fuel prices alone. You need to compare purchase or switching cost, real consumption, energy, maintenance and annual mileage; switching pays off when accumulated savings exceed the extra cost.

Would lower taxes automatically make diesel much cheaper?

A tax cut would mechanically reduce part of the price, but would not remove pressure on refining. In October 2026, the government was also considering using strategic diesel reserves, with an expected reduction of 12 to 18 cents per litre according to Alternatives Économiques.