Petrol vs diesel cars: which is the better choice?

Petrol and diesel cars aren’t dead and buried just yet. Okay, so there’s a ban on the sale of new petrol and diesel cars from 2035, but that’s in the distance rather than just around the corner. One day soon we may all be driving electric vehicles. But there’s life in the internal combustion engine for a while yet.

Conventional petrol cars make up around 56% of all new-car sales, and while diesel is far less popular than it once was, tens of thousands of diesel cars still find new homes each year.

It’s clear then, that despite the looming ban on sales of new petrol and diesel cars, these vehicles tick all the necessary boxes for millions of drivers. Our analysis will help you choose between petrol and diesel for your next car.

What’s the difference between petrol and diesel cars?

There are a number of key differences between petrol and diesel cars, both in terms of the ownership and driving experience, and with regard to legislation.

Purchase price

A diesel car is typically more expensive than an equivalent petrol in almost every case – although not always by much.

As an example, a petrol Mercedes E 200 AMG Line saloon has a recommended manufacturer price of £55,120 as of June 2024, whereas the diesel Mercedes E 220 d AMG Line is £56,820.

These higher purchase prices are down to a number of factors. One of these is that because diesels ignite fuel by compressing it to very high pressure rather than using a spark plug, the engines need to be stronger. Emission-control systems like diesel particulate filters and AdBlue also add to the cost.

Running costs

Vehicle running costs encompass a wide variety of factors, so we’ll take these one at a time.

Insurance: On insurance, the petrol vs diesel argument is roughly equal. A diesel car may have slightly higher insurance than an equivalent petrol due to potentially more expensive repair costs, but in general the difference isn’t that sharp.

Servicing: Again, diesel cars tend to have more systems (such as the emission-control ones mentioned above) than petrol cars, which can add to servicing costs, though often not by much. It’s worth highlighting that older diesel cars to have worse MoT pass rates than petrol cars, potentially meaning more expense down the road.

AdBlue: modern diesel cars use a system called Selective Catalytic Reduction and, in particular, a liquid known as AdBlue, to reduce harmful emissions of nitrogen oxides (NOx). AdBlue systems squirt tiny amounts of an ammonia-based liquid into the exhaust fumes to reduce NOx emissions, and AdBlue tanks periodically need refilling. An AdBlue tank might be 10 litres in size, and if bought online AdBlue costs around £20 for that amount.
Different cars and driving styles see AdBlue consumed at different rates, but it’s reasonable to expect 10 litres of AdBlue to last 3,000 to 6,000 miles, so the cost is relatively minor.

Fuel costs: This is where diesel fuel vs petrol starts to tip in favour of diesel. The petrol Mercedes mentioned earlier officially returns 44.2mpg, whereas the diesel E 220 d manages 58.9mpg, a 33% advantage. For high-mileage drivers, this improved fuel efficiency means a diesel car will gradually make up for any additional purchase and servicing cost it may entail over its petrol counterpart.

As an example, if a litre of petrol is £1.45 and a litre of diesel is £1.54, filling a 60-litre tank will cost a petrol driver £87 and a diesel motorist £92.40. But the E 200 driver would cover 583 miles on 60 litres, whereas the E 220 d driver will manage 777 miles. The petrol driver will spend 14.9 pence per mile on fuel, and the diesel motorist 11.9 pence, a saving of 3 pence per mile. Over 20,000 miles a year for three years, say (a high annual mileage for which a diesel car is well-suited) the diesel driver will have saved £1800.

To help you save money at the pumps, we’ve created a fuel price checker which finds you the cheapest petrol and diesel prices in your local area.

Emissions and tax: Older diesel engines are relatively polluting, but thanks to AdBlue and diesel particulate filters (DPFs – which trap soot from exhaust gases), modern diesels can be considered effectively as clean as their petrol siblings.

Diesel cars emit much less carbon dioxide (CO2) than petrol cars (this was partly why they used to be encouraged by previous car tax and company car tax regimes) than equivalent petrol cars, too. In fact, the current car tax system sees a car’s first-year rate determined by how much CO2 it emits, so while the E200 will cost £270 for its first year, an E 220 d will be £220 (2024/25 tax rates).

Company car tax remains determined by CO2 emissions, too, with the diesel E 220 d attracting a 30% Benefit-in-Kind rate, and the petrol E 200 a 34% rate (precise CO2 emissions and therefore tax costs will be affected by alloy wheel sizes and other factors, so do check figures yourself before any potential purchase).

It’s also worth highlighting that low emission zones such as London’s ULEZ (schemes are also starting to appear in other cities) are much tougher on diesel cars. Most such schemes allow petrol cars meeting relatively old Euro 4 emission regulations to enter zones without paying, whereas diesels must typically be Euro 6 compliant. This means, in practice, that a petrol car from 2006 is likely to escape any such charge, but a diesel would need to be much newer – from 2015 or so onwards – to avoid charges.

Driving and performance

There are differences between how petrol and diesel cars drive, but they’re not fundamental ones. We’ll take each in turn.

Noise: While diesel cars have become much more refined over the years, they’re still noisier than an equivalent petrol car (sports cars aside). Often described as a ‘clatter’, the sound produced by a diesel car tends to be less pleasing to the ear than that made by a petrol engine.

Revs/engine speed: Diesel cars have a lower rev limit (IE how fast the engine can spin) than petrol cars, typically having a maximum rpm (revolutions per minute) of 5,000, compared to the 6,500rpm a petrol car might have.

Power delivery/torque: Diesel cars produce less power but more torque than an equivalent petrol engine (think of power as how hard you push a spanner, and torque as how long the spanner is). This means that diesels are well-suited to towing caravans and the like, and also don’t need to be worked as hard to accelerate, particularly at speed. This easy torque and low-rev nature makes diesels excellent motorway cars, and also partly explains why they use less fuel.

Diesel particulate filters: DPFs absorb tiny particles of soot from a diesel car’s exhaust, trapping it in a filter. The trapped soot needs to be burned off (regenerated) periodically, which can only occur when an engine is up to operating temperature, and the car’s engine and road speed is above a certain level. Fail to regenerate a DPF when required and you risk allowing it to be blocked. This means people who predominantly drive in town and don’t often get above 50mph may be wise to consider a petrol, hybrid or electric car rather than a diesel. See our guide to DPFs for more information.

Pros and cons of petrol cars

Petrols tend to be cheaper and quieter than diesels, but not as fuel efficient.

Advantages

• Cheaper to buy
• No DPF to clog (although some petrol cars now have particulate filters)
• Engines are typically more refined
• Potentially lower servicing costs and better MoT pass rates
• Cheaper fuel

Disadvantages

• Higher fuel consumption
• Higher CO2 emissions
• Not so well suited to towing

Pros and cons of diesel cars

Diesels suit high-mileage drivers, but tend to be noisier than petrols and there’s less choice than there used to be.

Advantages

• Better fuel efficiency
• Longer range between refuelling stops
• Good motorway performance
• Engine doesn’t need to be worked as hard
• Lower CO2 emissions
• Well suited to towing

Disadvantages

• More expensive to buy
• Potentially higher servicing costs
• Older models likely to fall foul of emission zones
• Unappealing engine note
• Potential for clogged DPFs

The 2035 ban on petrol and diesel cars

The UK government has pushed back a ban on petrol and diesel cars from 2030 to 2035.

After this date, only zero-exhaust-emission vehicles (IE electric cars and hydrogen cars) will be allowed to be sold from new, banning both petrol and diesel cars from new-car showrooms.

All of this applies only to new cars, though: there is no indication that second-hand petrol and diesel cars will face any restrictions relating to their sale. The jury is out with regard to whether any fresh emission control standards will be introduced, though, as while new zones may be brought in, almost all current zones work on a basis of legislating against pre-Euro 4 petrol cars, and pre-Euro 6 diesels.

After the 4 July general election, this deadline may well change. To see what each of the main Great British political parties are promising drivers in their election manifestoes, check the links below.

Lib Dem Manifesto: 7 pledges for drivers
Conservative Manifesto: 10 things the Tories are promising drivers
Labour Manifesto: 6 promises for drivers

Should I go for hybrids or electric cars?

Oof, now you’re asking. That’s a tricky one, and there are so many variables to consider. Your budget, annual mileage, typical daily journeys and more all need to be considered.

Full hybrids (sometimes called ‘self-charging hybrids – in other words, hybrids that can’t be plugged in) are cheaper to buy than plug-in hybrids (which have bigger batteries and can go further running on electricity alone).

You’ll find that full hybrids may have official fuel economy to rival diesels and beat petrol cars. However, while a diesel tends to be at its best on a long motorway drive, hybrids are particularly economical around town where regular slowing and accelerating allows the batteries to recharge under braking.

Plug-in hybrids can be exceptionally economical, so long as you can recharge regularly and most daily journeys can be completed using electricity. They tend to be relatively thirsty on long journeys once the batteries are running low.

Maybe you’ve narrowed your choice to petrol hybrid vs diesel hybrid. Well, there are far more petrol hybrids than diesel hybrids, partly because it’s harder to reach the exhaust temperatures needed for a DPF to regenerate if the engine isn’t running all the time. Mercedes does offer diesel plug-in hybrids, though, which aren’t as thirsty on a long run as a petrol plug-in hybrid.

Electric cars are best-suited to drivers who install a charging point at home, as recharging on a domestic tariff is massively cheaper than using the public charging network. With each new generation of electric vehicle, charging speed and range is improving, but even the best EVs take longer to charge than a petrol or diesel takes to refuel.

This is such a complex subject that we have a dedicated advice guide: Should I buy and electric car. It is best to weigh up all the pros and cons of switching to an EV or remaining with petrol or diesel power.

If you are a company car driver, then the tax benefits of a plug-in hybrid or – better still – an electric car are compelling.

Petrol vs diesel cars FAQs

Do diesels last longer than petrol?

Diesel cars tend to suit high-mileage use because of their economy. For anyone who racks up motorway miles, diesels generally offer lower running costs than petrols.

For that reason you tend to find that a lot of really high-mileage used cars are diesels. That contributes to the reputation of diesel cars lasting longer than petrols, but to some extent that’s confusing cause and effect. Diesels are cheaper to run than petrols if you’re covering intergalactic mileage, but not necessarily more reliable.
In fact, most reliability studies show that petrols are more reliable than diesels, so there’s no reason a petrol can’t last as long as a diesel or longer.

With both petrol and diesel engines, sympathetic driving and regular maintenance will play a big part in how well the engines give trouble-free driving.

Is it worth buying a diesel car?

Diesels suit regular long-distance driving. They’re also great at towing trailers and caravans, as they pull better from low revs than petrols.

So yes, for the right buyer diesel power can still make sense. If you are shopping for a new car there’s a lot less choice than there used to be, but there are still many thousands of diesels for sale on the second-hand market.

If you mostly drive around town and don’t cover a high mileage, then a petrol, hybrid, or electric car should suit you better.

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