Petrol vs dieselPetrol and diesel fuel costs
Petrol or diesel?
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| Example running costs comparing a petrol with a diesel car | ||||||
|---|---|---|---|---|---|---|
| Example number | Car price difference | Annual fuel cost petrol | Annual fuel cost diesel | Annual CO2 emissions petrol | Annual CO2 emissions diesel | No. of years to recoup diesel price premium |
| 1 | £1,500 | £1,068 | £852 | 2.44 | 2.21 | 6.9 |
| 2 | £2,000 | £1,330 | £991 | 3.04 | 2.57 | 5.8 |
| 3 | £1,500 | £1,575 | £1,171 | 3.6 | 3.04 | 3.7 |
| 4 | £1,850 | £1,991 | £1,353 | 4.55 | 3.52 | 2.8 |
| 5 | £1,099 | £1,805 | £1,472 | 4.12 | 3.83 | 3.3 |
When buying a new car, you’ll usually get the chance to choose between petrol and diesel engines. And while you can be fairly confident the petrol model will be cheaper to buy, knowing which is going to cost you more in the long run is a bit more difficult.
This is because the overall running costs of petrol and diesel cars are affected by so many factors, including fuel prices, servicing bills, mileage and emissions-based charges.
The calculator on the right only takes initial purchase price, fuel costs and mileage into account, but should give you an idea of how many years’ driving it will take to make buying a diesel the most cost-effective choice - if indeed the diesel will ever be cheaper.
The 'diesel payback' period could take much longer than you would think - especially for lower mileage drivers. However, if the diesel car saves you money on car tax and depreciation, it may pay for itself sooner.
Fuel economy and emissions
Diesels use significantly less fuel than their petrol equivalents. Take the five-door, 1.6-litre Ford Focus Zetec as an example: the diesel version (£17,640 OTR) achieves a combined fuel economy of 62.7mpg, while the petrol model (£16,140 OTR) manages just 42.2mpg.
The Focus diesel’s emissions are lower, too – it puts out 119g/km of CO2, compared with the petrol’s 159g/km.
In this case, choosing the diesel Focus over the petrol version means you’ll reduce your impact on the environment and need to fill up less often. The downside, of course, is that diesel costs more at the pumps.
Fuel prices
In the UK, diesel can be more expensive than petrol. And although petrol cars often work out more expensive in the long run, it could take several years of fuel-efficient motoring to make buying a diesel worthwhile.
If you are planning to keep your new car for just a few years, or if you’re a low-mileage driver (less than 10,000 miles a year), make sure you use the petrol-diesel calculator on this page. You could actually save hundreds of pounds by opting for a petrol model.
Which? has put together a guide to help you find the cheapest petrol, diesel and LPG. If you're looking for a car with environmental credentials, read our reviews of green cars such as the Toyota Prius and Honda Civic Hybrid.
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