Diesel vs Petrol: Which is Cheaper to Run?
Diesel costs more per litre — but gets you more miles. Petrol is cheaper at the pump — but burns faster. The answer to which is cheaper depends entirely on how much you drive.
Cost examples below use illustrative prices, not today’s pump prices. Compare current local prices and the actual fuel economy of the cars you are considering.
Policy and tax sources
Diesel vs Petrol at a Glance
| Factor | Petrol | Diesel |
|---|---|---|
| Pump price | Check current local E10 | Check current local B7 |
| Fuel economy (typical) | 35–50 mpg | 45–65 mpg |
| Fuel duty | 52.95p/litre | 52.95p/litre |
| Vehicle Excise Duty (new cars) | Lower CO2 | Higher CO2 (older) |
| Engine cost / servicing | Cheaper | Slightly higher |
| Short journey suitability | Good | Poor (DPF issues) |
| Long journey efficiency | Good | Excellent |
| Best for mileage | Under 12,000/yr | Over 15,000/yr |
| Pure petrol/diesel new-car sales phase-out | 2030 | 2030 |
Illustrative family-car figures. Check Fuelr for current reported local prices.
The Maths: Break-Even Mileage
The question isn't just about fuel cost per litre — it's about cost per mile. Let's compare a petrol and diesel version of the same car:
Example: Family hatchback
Petrol version
- Fuel economy: 42 mpg
- Fuel cost: 133p/litre
- Cost per mile: ~14.3p
- Annual fuel at 10,000 miles: ~£1,430
Diesel version
- Fuel economy: 56 mpg
- Fuel cost: 140p/litre
- Cost per mile: ~11.3p
- Annual fuel at 10,000 miles: ~£1,130
At 10,000 miles/year: diesel saves ~£300 in fuel alone. But if the diesel car cost £1,500 more to buy, the break-even point is after 5 years of fuel savings.
The higher the annual mileage, the faster diesel pays back the initial premium. For drivers doing 20,000+ miles per year, the fuel saving alone is typically £500–£800 annually.
Other Costs Beyond Fuel
Fuel is the biggest running cost difference, but not the only one:
- Purchase price: Diesel variants typically cost £1,000–£2,000 more than petrol equivalents from new.
- Vehicle Excise Duty (road tax): Vehicle tax depends on registration date, CO2 and list price. Electric vehicles also became liable for VED from April 2025. Check the current DVLA rates for the exact car rather than assuming it is tax-free.
- Servicing: Diesel engines can be slightly more complex (DPF regeneration, AdBlue systems on Euro 6+). Some mechanics charge more for diesel servicing.
- AdBlue: Many modern diesel cars require AdBlue (diesel exhaust fluid) to meet Euro 6 emissions. A 10-litre top-up costs around £10–£15.
- Clean Air Zones: Older diesel cars (pre-Euro 6) face charges in UK Clean Air Zones in cities like Birmingham, Bristol, and Bath. Check before buying an older diesel.
Who Should Choose Diesel?
Diesel suits you if:
- ✓You regularly drive 15,000+ miles per year
- ✓You do mainly motorway or A-road driving (not urban stop-start)
- ✓You plan to keep the car for 5+ years
- ✓You tow a caravan, trailer, or boat (diesel torque is superior)
- ✓Your car is a larger SUV, van, or 4x4 where diesel mpg advantage is greatest
Diesel is not suitable if:
- ✗You mostly do short urban journeys (DPF blockage risk)
- ✗You drive under 10,000 miles per year
- ✗You live in or regularly drive through a Clean Air Zone with older diesel restrictions
- ✗You're concerned about the new-car sales phase-out and resale value
The Alternative: Petrol Hybrid
For some drivers, a petrol hybrid (HEV or PHEV) offers the best of both worlds: petrol simplicity with diesel-like efficiency. A typical petrol hybrid achieves 50–70 mpg in mixed driving, significantly cutting the fuel economy advantage diesel once had.
PHEVs (plug-in hybrids) can drive 20–50 miles on electric power alone, ideal for urban commuters. For drivers who can charge at home, PHEV running costs can rival or beat diesel. For pure long-distance driving without charge points, a petrol hybrid still wins over diesel for most mileage profiles.
Frequently Asked Questions
Is diesel cheaper to run than petrol?
It depends on your mileage. Diesel is typically 5–15p per litre more expensive than petrol, but diesel cars achieve 15–30% better fuel economy (more mpg). For high-mileage drivers (over 12,000–15,000 miles/year), diesel is usually cheaper to run overall. For lower mileage driving, petrol wins on running costs.
Will diesel cars be banned in the UK?
Government policy ends sales of new purely petrol and diesel cars from 2030, with all new cars and vans to be zero-emission from 2035. This concerns new vehicle sales, not a ban on driving or selling an existing car. Check current government guidance before making a purchase decision.
Why is diesel more expensive per litre than petrol?
Diesel and petrol pay the same fuel duty in the UK (52.95p/litre). The price difference is due to refinery processes and global demand. Diesel is used by HGVs, ships, trains, and for heating oil — global demand is very high. Refinery capacity for middle distillates (diesel range) is often constrained relative to demand.
What is the break-even mileage for diesel vs petrol?
As a rough guide, diesel becomes cost-competitive around 12,000–15,000 miles per year, assuming you drive a mix of motorway and town driving. The exact break-even depends on the price gap between diesel and petrol, your specific cars' mpg ratings, and any difference in purchase price between petrol and diesel variants.
Is diesel bad for short journeys?
Yes. Diesel engines need to reach operating temperature to function efficiently and to regenerate the diesel particulate filter (DPF). Frequent short cold journeys (under 5–10 miles) prevent the DPF from regenerating, which can cause it to block — an expensive repair. Diesel is best suited to regular longer journeys.
Should I buy a petrol or diesel car?
For lower-mileage or mainly short-journey drivers: choose petrol (or hybrid/electric). Diesel makes sense if you regularly drive 15,000+ miles per year, do mainly motorway/A-road miles, and plan to keep the car for 5+ years. Otherwise, a petrol hybrid or full hybrid often offers the best compromise on running costs and environmental impact.
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