Should you buy a petrol or diesel car?

  • Pros and cons of petrol and diesel explained
  • Taxation and other costs highlighted
  • Is petrol the better option for you?

Should you buy a petrol or diesel car?

There was a time not that long ago when diesel cars were popular with drivers. Impressive fuel economy figures and low carbon dioxide (CO2) emissions that resulted in cheap tax rates – especially for company car users – meant that there was a period at the start of the 21st century when diesel was the fuel of choice.

But fast-forward to today, and diesel isn't as desirable. Monthly sales figures reveal a steady decline in the number of new diesel cars leaving showrooms. While petrol power has claimed most of diesel's lost sales, plug-in hybrid and electric cars have taken their share, too.

The weight of public opinion is changing rapidly and research shows that the soot and particulates found within diesel exhaust gases are harmful to public health and the environment. so you could be forgiven for thinking that diesel has had its day.

Diesel vs petrol cars: which to buy?

Here we look at the pros and cons of diesel, and see how it stacks up against petrol power.

Diesel pros

Long-distance fuel economy
Diesel engines are more efficient than petrol ones because of the high energy content of diesel fuel. While petrol cars are closing the gap for efficiency, diesel is still a better choice for drivers doing lots of motorway miles.

Torque from low revs
Diesels are a favourite with drivers who tow trailers or caravans thanks to their torque characteristics. There is strong pulling power from low revs, so a diesel doesn't have to work as hard as a petrol to move heavy loads. Check out the Parkers guide to towing to learn more.

Low CO2 emissions
Compare a diesel engine with a petrol unit with the same power output and you'll see that the diesel emits less CO2. However, as with fuel economy, the difference is narrowing.

Diesel cons

Harmful particulate pollution
While CO2 emissions for diesels are favourable when compared with petrol, the soot produced by diesel engines is classed as a carcinogenic that's harmful to health. High concentrations of nitrogen oxide (NOx) and carbon monoxide (CO) also have an impact.

AdBlue top-ups needed

Modern diesels can only meet the latest emissions legislation by adding a special chemical mixture to the exhaust gases. Commonly known as AdBlue, it's a combination of urea and deionised water that needs to be topped up every few thousand miles or so.

Diesel costs
Expect to pay at least £1,000 more for a diesel over a similar petrol-powered car. Company car users don't get much of an advantage, either. Benefit-in-kind tax rates now favour all-electric or plug-in hybrid models over pure petrols or diesels, while the latest diesels are taxed at the same rate as petrol cars, so a higher list price will negate a diesel car's lower emissions. Road tax savings have also gone the same way, with both fuel systems now costing the same for annual Vehicle Excise Duty.

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Petrol pros

Lower fuel prices
There was a time when diesel was cheaper than petrol, but that hasn't been the case for a few years now. Wholesale prices are largely to blame, because unlike petrol there is demand for diesel across industries other than fuelling vehicles.

Smoother responses
If you're a driving enthusiast, then nothing beats the sound and power delivery of a petrol engine. There are no rattles or droning from the engine bay, just a smooth hum from under the bonnet and free-revving power.

Urban efficiency
If you do lots of short, low-speed trips, then petrol will be a better option. Diesel engines use a particulate filter to help reduce pollution, but this needs faster runs to keep it in top working condition. If you just do short journeys, it will get clogged and harm a diesel car's running. They’re expensive to replace, too.

Petrol cons

Shorter range
Pure-petrol cars are becoming more efficient, but on longer trips it's still diesel that leads the way. While the price of unleaded is cheaper than diesel, you'll be filling up more often, especially if you cover longer distances on a regular basis.

Environmental impact
Drilling for oil in all its forms is having a severe impact on the planet, while on a local level petrol is more hazardous than diesel to transport. If there's an accident involving a fuel spill, the chemicals in petrol are not only flammable, but they can cause damage to tarmac and harm wildlife. That's not to say that diesel is any less dangerous, as it can leave oil slicks when spilled, but it's not flammable like petrol.

Conclusion: diesel still has lots of advantages

Diesel hasn't quite had its day if you do high mileages or are towing, but the odds are gradually stacking up against it. However, while petrol is taking its place in the short to mid-term, its days are also numbered as the UK approaches the Government's deadline to ban the sale of new petrol and diesel cars by 2030.

Before then, expect hybrids and plug-in models to grow in sales, before electric cars finally take the lead in the new-car market.

Parkers car buying tools to help you on your way

Don’t forget to check out our Cars for Sale section for the latest deals on new and used cars. And when you come to sell your current car, make sure you get a free car valuation with us to ensure you get the right price.

If you’re considering buying your new car on finance, make sure you visit our car finance section for a quote - we work with over 20 lenders to give our customers access to more than 100 different lending options.

Further reading on Petrol vs Diesel

Read through our features on petrol vs diesel to help you decide: 

Video: petrol vs diesel vs hybrid Volkswagen Golfs