Petrol and diesel cars still make up the majority of UK car sales, despite gradually increasing electric car sales in the UK. Diesel engines have had a tough time in the press lately and, while some of the criticism is merited, there’s a lot of misinformation that’s led to some models being demonised unjustly.

To help you make the decision between petrol and diesel, we’ve outlined the costs and benefits of each fuel type below. Read on for more info or watch our resident car expert to break down the issues involved:

Petrol vs diesel: in a nutshell

• Many modern diesel cars are fitted with a diesel particulate filter (DPF), which can clog if you don't often drive at motorway speeds. It's a pricey fix, so best avoid diesels if you avoid motorways.
• Diesel cars tend to cost more to buy than an equivalent petrol car. In the past, it was possible to make this back thanks to diesel cars having lower car tax and fuel costs.
• Since the new car-tax change, from the second year of ownership you'll pay a standard rate of £140 a year. This means it will take you longer to recoup the higher on-the-road price you pay for a diesel car, as you will now only save between £105 to £125 on running costs per year (largely thanks to better fuel economy).
• Diesel cars also tend to be the fuel of choice for those who need to tow thanks to diesel engines producing huge amounts of torque (pulling power) - but petrol and hybrid alternatives are available.

Demonisation of diesel

There’s been a lot of bad press about diesel in recent months thanks to the VW emissions scandal, where real-world testing revealed that some cars’ emissions were far higher than they were when tested in lab conditions. It’s crucial to note that the problems outlined in this scandal affect older diesel models, and the fact modern diesels feature exhaust after treatment such as AdBlue and diesel particulate filters mean they’re fully compliant with the latest Euro6 emissions standards.

As a result of the scandal, a new test dubbed the Worldwide Harmonised Light Vehicles Test Procedure will come into effect in September 2017. This will produce more realistic figures for both diesel and petrol-powered cars in real-world environments along with removing the possibility the tests can be cheated.

Petrol vs diesel – emissions

Many car buyers in the early 2000s chose diesel vehicles because they produced less CO2 emissions than their petrol equivalents – road tax at the time was based solely on CO2 emissions so diesel cars tended to cost less. Diesel models produce more nitrogen dioxide and particulates than petrol ones, however, which can lead to acid rain, smog and respiratory problems in people. The recent changes in car tax and the current uncertainty over diesel models reflects an increased awareness of this environmental damage.

Modern diesel cars feature lots of technologies to minimise their environmental effects. These include diesel particulate filters that reduce the number of particles emitted from the exhaust. Some new vehicles use AdBlue – a urea-derived additive sprayed into the exhaust to break down some of the nitrogen dioxides.

One way to think about it is that petrol cars are worse for the environment thanks to their generally higher CO2 output, while diesel cars are worse for human health thanks to their greater particulate and nitrogen oxide emissions.

Petrol vs diesel – price

In general, a diesel car is more expensive than an equivalent petrol version. For example, the Renault Kadjar in Signature S Nav trim with a 130hp 1.2-litre turbo petrol engine costs £24,775, while the 1.5-litre diesel with only 110hp costs £26,745 – almost £2,000 more for a car with less performance. For an equivalent diesel with 130hp, you’ll be paying £27,965 – significantly more than the petrol. In this case, the 1.2-litre petrol averages 49mpg while the 1.5-litre diesel returns 72mpg.

Petrol vs diesel – economy

While diesel cars cost more to buy than petrol cars, they’re also more efficient. In our tests, we managed 55mpg and 35.4mpg in the diesel and petrol Kadjar respectively. With current fuel prices, you’d have to drive 38,000 miles to break even, so it’s worth considering how many miles you cover per year and how long you’re intending to keep the car before making a decision. Many lower mileage buyers could save money by buying a cheaper petrol car than a pricier diesel car because they won’t own the car long enough to take advantage of the fuel savings.

When you take tax and insurance into account, there’s very little in it with the 1.2-litre petrol and 1.5-litre diesel being in insurance group 16 and 15 respectively. In their first year, the diesel is just £20 cheaper to tax, then both cars cost the same £140 in subsequent years thanks to the 2017’s new tax regulations. Servicing costs for the two cars are identical, too.

Petrol vs diesel – running costs

 
Petrol engines, in comparison, typically don’t have as much pulling power as diesels, so have the be revved more to achieve the same performance. While they offer a marginally less grunt, petrol engines have much more top-end power that’s great fun to exploit if you’re driving hard and are generally smoother and more refined leading to a generally more hushed driving experience.

Diesel and petrol engines also feel very different from behind the wheel. Diesels provide very strong low-down pulling power which helps them feel relaxing to drive because you require fewer down shifts to generate meaningful acceleration. This low-down grunt also helps if you plan on using your car to tow or regularly carry lots of passengers in your car.Petrol vs diesel – driving

Petrol vs diesel – summary

Overall, it boils down to what you use the car for. If you cover high annual mileages, often tow or carry passengers on a regular basis we’d recommend going for the diesel. However, if the majority of your driving is around town and short journeys or you want a ‘sportier’ driving experience, petrol is the fuel to go for.