Petrol vs Diesel – which should you buy?

Although tax breaks and free parking incentives have tempted many drivers to make the move towards hybrid and electric vehicles, petrol and diesel engines still power the vast majority of cars on UK roads.

For the cost-conscious, hybrids may be too expensive and, for a commuter, the range of electric vehicles may be too limiting – could a fuel efficient diesel car offer an appealing solution to this dilemma? Or will a cheap petrol suffice for city dwellers?

If you’re considering a new car, let us help you weigh up the facts when it comes to the petrol versus diesel debate. Use our car chooser to help you pick your next car, then use our car configurator to see how much carwow could help you save.

Fuel economy

Modern diesel cars are often far more frugal than their petrol powered cousins. Taking three popular diesel cars cars of different sizes as examples we can see that a diesel Volkswagen Polo, Ford Focus and BMW 3 Series will consume on average 29 per cent less fuel than a comparatively powerful petrol alternative.

Fuel economy comparison
Volkswagen Polo 1.4-Litre TDI – 83mpg 1.2-Litre TSI – 60mpg
BMW 3 Series 320d – 56mpg 320i – 41mpg
Ford Focus 1.5 TDCi – 74mpg 1.0 ecoboost – 51mpg

With a drop in fuel economy of as much as 30 per cent, you can expect to be making significantly more trips to the service station in a petrol vehicle.

Running costs

Recently, the UK has experienced a sharp drop in the price of diesel which is now the same or cheaper than the average price of petrol – 110p per litre and 109p per litre respectively. This is a significant boost for diesel drivers everywhere who have historically had to shell out more to fill their tanks.

Road tax is another area where diesels excel. With engines able to emit far less carbon dioxide (CO2) per km, diesel cars fall in to cheaper tax bands. Some cars such as the VW Polo 1.4 TDI emit so little CO2 that they are exempt from taxation.


With the pressure of ever more restrictive emissions testing, manufacturers have had to spend more to develop cleaner diesel engines. This bill has unfortunately been passed on to the consumer – you can expect a new diesel powered car to cost noticeably more than a petrol alternative.

If you think cheaper running costs will outweigh a hefty price-tag, you may want to re-think your options. Take, for example, choosing a BMW 320d over a 320i – you’d need do drive over 80,000 miles in the diesel before the fuel savings start to overtake the higher purchase price. If you don’t plan on keeping your car for a very long time, petrol might be a better option.

On the road

For many drivers, the instant throttle response of a nippy petrol engine simply cannot be out-done. Although diesels have improved immeasurably in recent decades, the more limited rev-range and emphasis on torque rather than power means they are often much happier as motorway cruisers than B-road blasters.

If you travel long distances and are happy to flick on cruise control and let the car do the work for you then a diesel makes a lot of sense. Levels of refinement are now comparable to petrol engines, especially when cruising, and many manufacturers will tailor their diesel models for this very role.

At the finest level, however, petrol cars are still more refined and, by virtue of their combustion process, they sound better when accelerating. Equally, where petrols used to feel ‘gutless’ compared to their torquey diesel rivals, modern turbos mean petrols can provide comparable levels of thrust.


Diesel engines naturally emit more sooty particulates than a petrol engine so, to ensure such chemicals are not simply released into the atmosphere, a filter is employed to “catch” them before they leave the exhaust system. By raising the temperature of this unit at regular intervals – often at higher speeds – these particulates can be burnt off and released.

If a car is only used for shorter, slower journeys however, this diesel particulate filter can become saturated and unable to burn-off the material it contains. To avoid this, modern diesels should be taken on the motorway about once a week. Should a replacement part be needed, you may be awaiting a very large garage bill.

Recent concerns

Manufacturers have worked hard to shake the reputation for diesels being noisy, smoky and dirty engines which should be confined to the commercial vehicle world. Since the Volkswagen “defeat device” scandal it is an image which has reared its ugly head once again.

It’s important for buyers to note that the issue is currently only affecting engines built to Euro 5 specification, not the latest Euro 6 requirements so modern diesel buyers needn’t fear that their car is polluting more than advertised. Manufacturers of diesel vehicles, however, once again face an uphill struggle in regaining the trust of consumers.


Although the choice between petrol and diesel has never been an easy one, the constant battle between these two fuels has forced manufacturers to improve with each new generation.

As consumers, we’re now spoilt for choice with a selection of varied engines which excel in different situations. If you regularly travel long distances and want a refined vehicle that won’t force you to stop for fuel every few hundred miles, then diesel may be the way to go.

If you’re looking to save on the total cost of ownership and don’t plan on keeping your car for extended periods of time, however, then a petrol is likely to be the better option. Petrols also tend to be more suited to enthusiasts and city drivers who only travel short distances.

What next?

If you’re still not sure which is the car for you, have a look at our car chooser and deals pages and let carwow find you a great deal on a new car. Once you’ve found the one you want, put it in our car configurator to see how much carwow could help you save.

Volkswagen Polo

A quality supermini with engines to suit all needs
£11,830 - £20,445
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BMW 3 Series

Smart saloon is one of the best all-round cars on sale
£25,580 - £41,435
Read review Compare offers

Ford Focus

A family hatchback that's fun to drive
£19,095 - £31,395
Read review Compare offers
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