Diesel was 19.82p per litre dearer than petrol in the official UK average for 10 August 2026. Petrol averaged 162.15p, while diesel reached 181.97p. A 55-litre diesel fill therefore cost £10.90 more than the same volume of petrol. The figures come from the Department for Energy Security and Net Zero, or DESNZ.
The gap does not come from a higher diesel duty rate. Both fuels carried 52.95p per litre of duty and 20% VAT that week. The main differences sit before tax, in wholesale product costs, refining conditions and supply. Retail pricing delays and local competition can then widen or narrow the amount seen at one forecourt.
Why Is Diesel More Expensive Than Petrol Right Now?
The official 10 August averages were 181.97p for diesel and 162.15p for petrol, a 19.82p gap (DESNZ, 2026). Diesel costs more because its wholesale product market faced stronger pressure, while retail diesel prices also adjusted more slowly after some wholesale falls.
A litre at the pump contains several costs. Crude oil is only the starting material. Refineries turn crude into separate products, including petrol and diesel. Each product then has its own traded price. Storage, biofuel blending, transport, duty, retailer costs and VAT complete the price.
That structure explains why petrol and diesel do not move together. A change in crude affects both, but demand and supply for each finished fuel can differ. Refinery output cannot always switch quickly enough to match those separate needs.
The Competition and Markets Authority, or CMA, found especially large wholesale increases for diesel during March and early April 2026. It said elevated wholesale costs explained most pump price increases during the period. The report also found that diesel retail prices later responded more slowly to falling wholesale costs.
The 19.82p gap is best read as a product-market difference, not an oil-price difference. Petrol and diesel share crude oil, tax rules and much of the delivery network. Their finished-product costs can still separate sharply before they reach the same forecourt.
How Is a Litre of Diesel Priced at the Pump?
Fuel duty was 52.95p per litre for both petrol and diesel on 10 August, with 20% VAT applied to both (DESNZ, 2026). Tax therefore adds heavily to each pump price, but the equal rates do not create the diesel premium.
The pre-tax fuel cost covers several moving parts:
- Crude oil: The refinery's raw material.
- Refining spread: The difference between crude and the wholesale finished product.
- Biofuel content: Diesel includes renewable components with their own market prices.
- Exchange rate: International oil products are commonly priced in US dollars.
- Distribution: Fuel must be stored and delivered to each forecourt.
- Retail spread: The station covers operations and earns its margin.
VAT makes a pre-tax gap larger because it applies as a percentage. If diesel has a higher product cost before VAT, the final gap includes VAT on that difference. However, VAT is not a separate diesel surcharge. The same 20% rule applies to petrol.
What should drivers remember? A national pump gap can change even when duty stays fixed. Finished-product markets and retailer timing often move faster than tax policy. This is why a crude oil headline cannot predict an exact pump price.
The CMA defines the refining spread as the difference between crude oil and wholesale petrol or diesel. Its road fuel review found that demand shocks, supply shocks and restricted refining capacity can increase those spreads. The concept remains useful, although the 2022 report does not explain every event in 2026.
Why Did Wholesale and Refining Conditions Hit Diesel Harder?
Between May and June 2026, average diesel fell 23p per litre as crude costs fell 10p and diesel refining spreads fell 11p (CMA, 2026). Those large movements show that the diesel product price had more room to fall after earlier supply pressure.
The UK depends more heavily on imported road diesel than imported petrol. The CMA's 2022 review found that imports supplied about 57% of road diesel in 2021, compared with around one quarter of road petrol. These older figures describe the market structure, not an exact 2026 share. They still show why international diesel supply matters greatly to UK prices.
Refineries produce several fuels from one barrel. Their output mix has limits. Stronger demand for middle distillates, which include road diesel, heating fuels and some industrial products, can raise diesel's finished-product price. A refinery cannot simply turn every petrol molecule into diesel when the market tightens.
Seasonal demand can influence middle-distillate markets, but it should not be treated as the proven cause of this August gap. Current UK evidence points more clearly to wholesale volatility, refining spreads, inventory decisions and delayed retail pass-through. A broad seasonal claim would hide those measured factors.
A falling diesel price can coexist with a large petrol gap. Direction and level are different questions. Diesel fell sharply from its spring peak, yet its finished-product cost remained high enough to stay almost 20p above petrol in August.
Did Retailers Keep Diesel Prices Higher for Longer?
The CMA found that lagged diesel spreads stayed above pre-conflict levels until the end of June 2026 (CMA, 2026). This suggests some retail diesel prices responded more slowly after wholesale costs fell, although normal purchasing and inventory delays explain part of the lag.
Forecourts do not all buy fuel at the daily spot price. Contracts, delivery dates and stored inventory mean the fuel sold today may reflect an earlier wholesale cost. The CMA used a two-week lag as a working measure, while noting that real arrangements vary by retailer.
The regulator found no evidence that retailers actively changed pricing strategies to exploit the crisis. That distinction matters. It did find continued high margins and passive pricing among many retailers. Some non-supermarket sellers gained from falling wholesale diesel costs but did not immediately cut prices to win market share.
Is every slow price cut unfair? Not necessarily. A retailer may still be selling stock bought at a higher cost. Yet prolonged slow pass-through can weaken competition. The CMA plans further work on retailer pricing and wholesale cost pass-through in its autumn report.
In May and June, average retail margins were 11.0p and 11.2p per litre. The June figure sat 0.5p above the 2025 average. Non-supermarket margins rose to 12.0p in June, while supermarket margins fell to 10.4p. These averages do not describe every company or station.
How Much Does the Diesel Gap Change by Forecourt Type?
PetrolPal's 20 August live sample averaged 182.14p for diesel and 161.15p for unleaded, a 21.0p gap across almost 8,000 priced observations per fuel (PetrolPal, 2026). Supermarket diesel averaged 179.08p, while branded forecourts averaged 183.85p.
The live station-type difference was 4.77p per litre for diesel. On a 55-litre fill, that equals £2.62. Petrol showed a 3.58p supermarket-to-branded difference, worth £1.97 on the same volume. These calculations use national groups, so a local search remains necessary.
Independent diesel averaged 182.14p in the same snapshot. That sat almost level with the overall diesel average. Individual independent stations can still beat nearby supermarkets, because national brand groups hide local pricing decisions.
The CMA reported potential savings of up to £9 per tank from shopping around in its May monitoring update. That is an upper local example, not a promised saving for every fill. Your actual result depends on nearby prices and the litres bought.
Why can towns differ so much? Competition, delivery costs, motorway locations, land costs and retailer strategy all play a part. National averages explain the market direction. They cannot tell you which forecourt is cheapest near your route.
Compare Petrol and Diesel Prices Near You — Search current fuel prices across the UK before you fill up.
What Can Diesel Drivers Do About the Price Gap?
A 19.82p gap adds £9.91 to 50 litres and £10.90 to 55 litres, using the official 10 August averages (DESNZ, 2026). Drivers cannot choose petrol for a diesel engine, but they can reduce the local premium they pay.
Start with these steps:
- Compare diesel prices before the fuel warning light appears.
- Check stations already on your planned route.
- Multiply the price gap by the litres you expect to buy.
- Reject detours that cost more than the gross saving.
- Compare supermarket, independent and branded options locally.
- Check the recorded price time before a long diversion.
Use a simple calculation: saving in pounds = pence-per-litre gap × litres ÷ 100. A 5p local gap saves £2.50 on 50 litres. A 10p gap saves £5. Driving several extra miles can remove part of that benefit.
PetrolPal tracked 8,077 UK stations at 05:03 UTC on 20 August. Its data source was the UK Government Fuel Finder service. Fuel Finder requires retailers to report price changes within 30 minutes, although an older timestamp can simply mean the price has not changed.
Could buying less help? Yes, when prices are unusually high and you expect near-term movement. A partial fill preserves flexibility. Do not run the tank dangerously low for a small possible saving.
Plan a Lower-Cost Diesel Stop — Compare fuel stops along your route before a longer journey.
Will Diesel Stay More Expensive Than Petrol?
Road diesel demand in 2024 was 16% below 2019, while petrol demand was 6% higher (DESNZ, 2025). That long-term shift does not guarantee a smaller diesel premium, because global product supply and refining conditions can outweigh UK road demand.
The gap can narrow when diesel wholesale costs fall faster than petrol costs. It can widen again if middle-distillate supply tightens, refinery output falls or international demand strengthens. Retail purchasing lags can delay either move at the pump.
The CMA's August report offers a useful warning against simple forecasts. Diesel fell 23p during May and June, far more than petrol's 6p fall. Even so, diesel remained much dearer in August. A rapid fall does not automatically remove a high starting premium.
Watch three signals instead of one prediction. Follow official DESNZ weekly pump prices, current local Fuel Finder data and future CMA analysis of wholesale pass-through. Together, they show the national gap, your local choice and whether retail prices follow costs promptly.
The official diesel premium was 19.82p per litre on 10 August 2026, while PetrolPal's live gap was about 21.0p on 20 August (DESNZ, 2026). These answers explain the most common tax, fuel-quality and saving questions.
