Petrol vs dieselChoosing between petrol and diesel

Car tax

Diesel VW Polo BlueMotion: exempt from road tax

Because diesel engines are so much more efficient than their petrol opposites, they’re often met with lower car tax charges.

The 1.4-litre diesel VW Polo BlueMotion, for instance, is exempt from car tax charges under current rules. But the equivalent, 1.4-litre petrol VW Polo is hit with an annual bill of £120.

Servicing costs

Diesels have a reputation for being more expensive to service, although they can often go longer between services than petrol models, which helps to offset this. However, over a typical three- or four-year ownership period, you're unlikely to see a significant difference between servicing costs for equivalent petrol and diesel cars.

Diesels tend to have lower emissions than petrol cars

Residual values of petrol and diesel cars

Finally, it’s important to consider what your car will be worth when you come to sell it. After all, depreciation can be one of the biggest costs of buying a new car.

Diesel cars generally retain their value better than petrol versions. They’re currently in high demand, thanks to people looking for cars with better fuel economy and diesel cars' lower car tax rates. Besides, many people hold onto the belief that diesel engines stay reliable for longer.

In reality though, modern, hi-tech petrol engines are likely to be just as reliable - and probably cheaper to repair if anything serious goes wrong.

Petrol cars are not always quicker than modern diesels

Petrol v diesel – other factors to consider

Leaving money aside, there are several other main differences between petrol and diesel cars that may influence your decision.

Conventional wisdom says that petrol models tend to be faster, smoother and quieter than their 'taxi-like' diesel counterparts, albeit less frugal.

But while diesels still tend to be more vocal, recent advances in diesel technology have made them much more refined and, when it comes to acceleration, the latest turbocharged diesels often match or beat similar petrol cars. Diesel engines also offer increased torque (pulling power) from low revs, which is especially useful when towing or overtaking.

Diesel cars use less fuel for a given mileage and are consequently less damaging to the environment (especially if fitted with a diesel particulate filter to trap the nasty soot-like emissions many associate with diesels). 

You can find out more about alternatives to petrol and diesel in the Which? Car guide to green car technologies.

Diesel cars winning the war?

VW's Golf MkVI has smaller, turbo petrol engines

As you can see, if you don't already drive a diesel car, there are many reasons to consider doing so - just don't automatically assume it will work out cheaper in the short run.

Diesel car sales may still be rising in the UK, but the war isn't won - the majority of us still drive petrol cars and, for low-mileage drivers, that's probably no bad thing. 

With the huge global demand for diesel fuel, carmakers may now return their attention to improving petrol engines - making then more fuel efficient and, indeed, drawing inspiration from the recent advances made on diesel engines. 

We've already seen a shift towards smaller, turbocharged petrol engines in cars like the Fiat Bravo and new VW Golf, which have replaced larger conventional petrol units. So the petrol v diesel debate looks sure to continue for a while yet...