Why Is Diesel More Expensive Than Petrol in the UK?
Diesel is more expensive than petrol in the UK — and has been for most of the past two decades. If you drive a diesel car, you'll know that filling up typically costs more per litre than unleaded petrol, even though diesel engines are generally more fuel-efficient. The reasons sit across refining, taxation, global demand, and market structure.
Here's a clear explanation of every factor involved.
Why Is Diesel More Expensive Than Petrol? The Key Reasons
1. Refining Costs Are Higher for Diesel
Crude oil is refined into multiple fuel products simultaneously — petrol, diesel, aviation fuel, heating oil, and others. Diesel requires more complex processing steps than standard petrol to meet modern fuel quality standards.
In particular, ultra-low sulphur diesel (ULSD) — the standard road diesel sold at UK forecourts — requires additional hydrodesulphurisation treatment to reduce sulphur content to the levels required under EU and UK regulations. That extra processing adds cost before a single drop reaches a forecourt.
2. Global Demand for Diesel Is Structurally High
Diesel is the fuel of choice for freight, logistics, shipping, agriculture, and construction worldwide. Trucks, trains, and heavy plant all run on diesel — meaning global demand is enormous and constant.
This sustained industrial demand puts upward pressure on diesel prices independent of what's happening in the passenger car market. When global freight activity rises — during economic recoveries or supply chain surges — diesel prices typically feel it first.
3. The Same Fuel Duty Applies to Both
It's a common assumption that diesel is taxed more heavily than petrol. In fact, both petrol and diesel carry identical fuel duty in the UK.
As of 2026, fuel duty stands at 52.95p per litre for both road fuels, following the freeze that has been maintained since 2011 (with brief exceptions). VAT at 20% is then applied on top of the pump price including duty.
Fuel duty alone accounts for roughly a third of what you pay at the pump. The gov.uk fuel duty rate table confirms the parity between petrol and diesel taxation.
4. Seasonal Demand Spikes for Heating Oil
Diesel and domestic heating oil (kerosene) are closely related products derived from the same crude oil fraction — middle distillates. In winter months, demand for heating oil increases, which competes with diesel supply and can push diesel pump prices higher.
This seasonal effect is one reason the diesel-petrol price gap often widens slightly in autumn and winter.
5. Supply Constraints and Refinery Capacity
Europe has historically had a structural imbalance in refinery capacity — better set up to produce diesel than petrol, partly because European car fleets skewed heavily diesel for many years. However, as diesel car sales have declined following emissions scandals and stricter regulations, this balance is shifting.
The RAC has noted that global refinery capacity constraints — particularly following the reduction in Russian diesel exports after 2022 — tightened diesel supply significantly and pushed European diesel prices to multi-year highs. While prices have since moderated, the episode demonstrated how exposed diesel pricing is to supply-side shocks.
How Big Is the Diesel-Petrol Price Gap?
The gap fluctuates but has typically sat at 3–8p per litre in favour of petrol under normal market conditions. During periods of supply stress, this has widened to 15–20p per litre.
To track the current gap at forecourts near you, compare local fuel prices in real time across thousands of UK stations.
Does Diesel's Better Fuel Economy Cancel Out the Higher Price?
Often, yes — for higher-mileage drivers. Diesel engines are typically 20–30% more fuel-efficient than equivalent petrol engines, meaning you travel further on each litre.
For a driver doing mostly short urban journeys, the efficiency advantage shrinks — diesel engines take longer to reach optimal operating temperature and the frequent cold starts reduce real-world mpg gains. For motorway-heavy drivers covering high annual mileage, diesel's efficiency advantage usually outweighs the higher pence-per-litre cost.
The AA provides a useful rule of thumb: diesel tends to make financial sense for drivers covering more than 12,000–15,000 miles per year on a mix of roads, assuming normal pump price differentials.
Will Diesel Prices Ever Fall Below Petrol?
It's possible but historically rare. The structural factors — higher refining complexity, global industrial demand, middle distillate competition — consistently push diesel above petrol.
As EV adoption grows and diesel car ownership declines, some analysts expect diesel demand to soften, which could gradually narrow or close the gap. For now, diesel drivers should plan for the premium to continue.
Practical Takeaways for Diesel Drivers
- Diesel costs more per litre due to refining complexity, global industrial demand, and seasonal heating oil competition — not higher taxation
- Fuel duty is identical for petrol and diesel at 52.95p per litre
- The price gap is typically 3–8p per litre but can widen significantly during supply shocks
- Diesel's fuel economy advantage can offset the price premium for drivers covering 12,000+ miles per year
- Supermarket forecourts consistently offer the lowest diesel prices — worth checking before every fill-up
Frequently Asked Questions
Why is diesel more expensive than petrol in the UK?
Diesel costs more due to higher refining complexity (ultra-low sulphur processing), strong global industrial demand from freight and logistics, and competition for middle distillate supply with heating oil. Taxation is identical for both fuels.
Do you pay more fuel duty on diesel than petrol?
No. Fuel duty is identical for both — 52.95p per litre as of 2026. The higher pump price for diesel reflects refining and market factors, not a higher tax rate.
Is it cheaper to run a diesel or petrol car?
It depends on mileage. Diesel engines are typically 20–30% more fuel-efficient, which can offset the higher per-litre cost for drivers covering 12,000–15,000+ miles per year. For low-mileage or urban drivers, petrol is often cheaper overall.
Why did diesel prices spike so much in 2022–2023?
Reduced Russian diesel exports following sanctions significantly tightened European diesel supply. The RAC reported that this supply shock pushed diesel prices to multi-year highs, with the diesel premium over petrol widening sharply before gradually easing.
Will diesel prices come down relative to petrol?
Potentially over the long term, as diesel car ownership declines and industrial demand shifts. In the near term, structural factors — refining complexity and global freight demand — are likely to keep diesel above petrol at the pump.