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Diesel or petrol: which is best for you?

Matt Fernell photo
Written by Matt Fernell, Financial Content Writer

2 January 2019

We weigh up the pros and cons of both types of fuels to help you decide which will be the most cost efficient for your particular needs.


Basic research will reveal that on average a diesel car can cost around £1,400 more than its petrol equivalent.

In the second-hand market, choosing a diesel engine model over petrol begins to make more sense. There's a couple of reasons for this:

  1. They tend to be more in demand because of their reputation for providing better economy and having lower tax rates thanks to their lower CO2 emissions.

  2. The perception that diesel engines are more reliable than petrol ones.

You are also likely to find that your brand new diesel has retained more of its value when you come to sell it on.

if you are buying new, consider the cost of servicing your car. Although the period between services tends to be longer for diesel engines, the cost of the parts are often higher.

Petrol engines need to be serviced at shorter intervals, but the parts are cheaper.

AA website - Motoring costs


The old perception that diesel engines are noisier, slower and dirtier than their petrol equivalents no longer holds quite as true.

A new generation of turbo engines are proving to match petrol ones in terms of performance, smoothness and noise levels.

Diesel engines are also able to produce high torque at low speeds and so are good for overtaking.


Diesel engines generally get you an average of 15 to 20% more miles per gallon than their petrol equivalents (depending on how they are driven).

But be aware that petrol engines are catching up in terms of mileage by using smaller, more efficient, turbo-charged engines.

Environmental impact

Diesel's greater efficiency means that its CO2 emissions are 20% lower than petrol.

However, diesel does produce a harmful by product in the form of tiny particles which have been linked to breathing disorders like asthma.

Manufacturers attempted to tackle this by fitting vehicles with particle filters and catalytic convertors, but ironically this has caused some reliability issues with certain models.

Petrol vehicles are closing the gap in terms of environmental impact by using hybrid engines. The introduction of sulphur-free petrol will help further reduce the environmental impact of petrol.

Tax and duty

Diesel's lower CO2 emissions means that diesel drivers are rewarded with lower tax bands than petrol owners.

Unfortunately, the government's generosity towards diesel does not also extend to fuel duty.

Hauliers have been lobbying parliament for a reduction similar to road tax in fuel duty on diesel to reflect its greener credentials.

AA website - Car tax

What alternative fuels are there?

There are alternatives out there to petrol and diesel, such as:

  • Liquid Petroleum Gas or LPG: It's half the price of diesel or petrol and has lower CO2 emissions. Most petrol engines can be converted to run on LPG. This means your engine can run on both petrol and LPG. However LPG has limited availability and poor fuel economy.

  • Biodiesel: Biodiesel can be used with a little modification to the engine. Like LPG an advantage is that it has very low carbon emissions but also suffers from a lack of availability.

And the winner is?

Both diesel and petrol offer their own unique advantages to the motorist.

Diesel's superior fuel consumption is a big selling point, but because of the higher cost of diesel cars it only if you clock up over 15,000 miles a year.

If you are a low-mileage driver it makes less sense to switch to diesel, as you are unlikely to feel any short-term benefits.

The gap between the two in terms of performance, efficiency and environmental impact is narrowing continuously.

Soon your decision could come down to little more than personal choice - say, choosing diesel to reduce your carbon footprint while accepting that you'll be paying more at the pump

Car insurance is just one of the costs of keeping your car on the road along with tax, petrol and servicing, so cut your insurance costs by comparing the best deals for you.

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