The great debate: petrol vs diesel

If you’re considering a new car, and have already taken electric power out of the equation (maybe you need to do lots of miles and electric power won’t work for you yet), then you need to make a difficult decision: petrol or diesel?

The debate has raged for decades now, as these two types of fuel offer distinct advantages and disadvantages. Before you buy a new car you may want to get a handle on what your car is worth, for example using the online Parkers valuation service, but once you’re done that and are ready to trade in, you need to work out whether to go for petrol or diesel.

There are benefits and drawbacks to both fuel types so in this article we’ll look at them all, so you have all the information to make an informed decision next time you buy a new car. We can’t make the decision for you, as it really depends on what you are planning to do with your car – the miles you drive, where you drive and what you do with the car. So read on to get all the info and then you’ll be prepared.

Fuel economy and tax

The first thing to be aware of is that diesels tend to be more economical than equivalent petrol units. They tend to work best at a constant throttle on the motorway, so if you do a lot of miles then diesel will probably be cheaper to run.

You have to factor in a couple of things, though. Firstly, diesel is more expensive than petrol at the pumps, so the fuel savings are only significant over many miles – and modern petrol engines are now so efficient that it can take longer for diesel to pay off.

The official fuel economy figures from WLTP are to be taken with a grain of salt, as they are rarely true to real life conditions and few cars can match them in normal driving. They can be taken as a baseline comparison figure but don’t expect to reach them without some serious effort driving smoothly and efficiently.

Diesels are also taxed higher than petrol when it comes to company car tax, although their low CO2 emissions mean that they are sometimes not that much more than petrol cars. It’s all in the details, so do your sums before you buy. If you don’t pay company car tax, then there’s no issue here as petrol and diesels will cost the same in VED or road tax (£150 a year plus a surcharge for models over £40,000).

Prices and emissions

Diesels produce some harmful tailpipe emissions, but so do petrol cars. All modern engines have to meet strict emissions laws, so they’re much cleaner than they once were – yet petrol engines are considered to be cleaner than diesels. For example, diesels over a certain age are charged extra to enter parts of London, but petrols of the same age aren’t.

Diesels tend to cost more to buy than petrols, and they also don’t sell at the same prices when second-hand. Petrols hold their value better, so diesels can sometimes lose out financially because of heavy depreciation.

Petrol and diesel for your needs

Do you drive on local roads most often, or is the bulk of your time in the car spent on the motorway? The answer to this question is probably the biggest indicator to whether you choose petrol or diesel power. Diesels are very efficient at high speed, but petrols are cleaner and cost less to run if you do fewer miles per day.

There are other factors at play, though. Petrols are smoother than diesels in most cases, so they’re quieter and more enjoyable to drive with. Diesels have punchy power delivery from very low revs, though, so if you don’t like to rev your engine then you might prefer a diesel for its low-down torque.

Diesel cars often have large fuel tanks, so if you hate filling up, you might want a diesel for the long driving range. On the other hand, you might want a car that gets up to temperature quickly for cold days, in which case a petrol would work better.

Ultimately you need to work out what’s most important for you in a car before you can decide which is the best fuel type for you. The short version is that if you do lots of miles then diesel will be cheaper to run but cost more to buy, while petrol makes sense for shorter trips and is more pleasant to use.


Award-winning writer, blogger, social media consultant and charity campaigner. Social Media Manager for BritMums, the UK's largest parent blogging network Freelance clients include Firefly Communications and Save the Children UK. Works with brands on marketing projects. Examples include Visit Orlando, Give As You Live, Coca-Cola and Kodak. Cambridge Law graduate with many years experience working across three sectors in advice, media relations, events, training and project management. Available for hire at affordable rates.

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