Carsnip Basics: Petrol Vs. Diesel

It feels like an age old question doesn’t it? Petrol vs. Diesel. Which one should you buy?

No matter who you ask they will have an opinion; some people swear by Diesels and think everyone should have one, and yet others would never touch one. The truth of the matter though? It very much comes down to your usage as the driver – one fuel type is better for certain categories of driver and the other for another. 

Let’s take a look at some of the main positives and negatives of each fuel type – and then afterwards there will be a short summary of questions for you to run through, and by answering them it SHOULD give you a good idea of which is the best purchase for you. This does however very much rely on you knowing your projected usage and being able to guesstimate fairly accurately – and I appreciate this can be difficult for most people!

This is quite a dry subject, so i think snappy bullet points are the way to go:


  • Is usually cheaper to purchase than diesel (pennies against the litre)
  • Cars are often a little cheaper to purchase in the first place
  • Cars are often slightly cheaper to service
  • Cars usually have a higher VED (tax bracket) than diesels
  • Cars have higher Co2 emissions, but emit less Nitrogen and other harmful products.
  • Engines have to be worked ‘harder’ by cycling through gears more – for example if overtaking or increasing speed on the motorway
  • Engines themselves run a little more smoothly (due to the burning of the fuel) and are therefore usually quieter
  • Engines are less fuel efficient, particularly the higher the capacity (for example in 5.0L vehicle vs. a 1.4L)


  • Is often more expensive to purchase than petrol (pennies against the litre)
  • Cars are often more expensive to purchase in the first place
  • Cars are often slightly more expensive to service
  • Cars usually have a lower VED (tax bracket) than petrol – BUT this is no longer as pronounced a gap since recent legislation has increased the VED for a lot of newer diesels
  • Cars produce lower Co2 emissions, but emit more other pollutants
  • Engines produce more torque making overtaking easier – the increased level of torque means les gear changes are necessary
  • Cars are more efficient – more miles from the equivalent amount of fuel
  • Cars best for motorway cruising
  • Vehicles have ‘DPF’ Diesel Particulate Filter fitted to them (more on this below)
  • Vehicles are sometime penalised by the ULEZ and other driving charges within certain cities

So a little quiz to help you decide:

  1. Do you drive more than the average person (12,000 miles per annum)?
  2. Do you do a lot of motorway or A-road miles (I.E. cruising at a steady speed)?
  3. Do you see driving as ‘a means to an end’ rather than a fun activity?

If your answer to 2 or more of these questions is yes, then there is a high chance that a diesel is right for you. If your answer to 2 or more of these questions is no, then the chances are that a petrol may be more appropriate. Obviously this is just a rule of thumb to point you in the right direction – and you should do your research to ensure that you are definitely picking the correct option. 

Bear in mind that from 2008 it became a legal requirement for Diesel cars to have a DPF fitted – a device that captures and stores exhaust soot (created by diesel engines). This device then burns this stored soot off when driving at higher (and steady) speeds; called the ‘regeneration process’. It is for this reason that city/town drivers usually are recommended to opt for a petrol, as they do not use their cars in a way that will activate the regeneration process often enough. This will eventually lead to the DPF becoming blocked – which will cause you to fail an MOT. Replacing a DPF can cost between £1000 and £3500 – making any savings made from cheaper diesel prices irrelevant if you end up in this situation. More info on DPF’s HERE.

A DPF Warning Light (left) and a diagram of a DPF (Right).

So in summary, the Diesel is not dead (as some are claiming). It is very much alive, and will continue to be so for many years to come. Manufacturers are slowly beginning to phase Diesel out of their product development in favour of Electric and Hybrid drive-trains, but the Diesel cars you may look to buy today still have way more than a car’s average life expectancy ahead of them before there are serious changes. See our summary of the Ban on Internal Combustion for more information on this!

Helpful Hints:

  • For the best fuel prices near you, use Petrol Prices! This summarises in real time what forecourts in your area are offering the best prices on the fuel you need.
  • Use the Money Advice Service’s ‘Car Cost Calculator’ to help you establish the running costs of your car (or the car you are looking to buy). This should help you to make an informed decision.
  • Break out an old fashioned Excel spreadsheet, and do some calculations! Put your current car on there, and put some choices of cars that you are looking at too. Then do your research and find out all of the relevant figures (including Annual Tax, MPG etc); and input them to compare.
  • Use an MPG Calculator to work out the relative costs of fuel of any vehicle during ownership (you will have to assume total mileage and an average fuel price).
  • Take a look at the Honest John: Real MPG site. This can sometimes give you a more accurate expectation of the real-world MPG of the car you are looking to buy – remember that manufacturer provided figures are derived from test conditions that are near-impossible to replicate in the real world. The MPG’s on this website are user-submitted. 
  • Use our ‘Natural Language’ search engine to find your next car! If this article has helped you realise that what you need is a diesel because you spend a lot of time on motorways, plus you know you need 4 doors and prefer an automatic in black; then you can go to our search engine that hosts over 500,000 cars and type “Black Diesel 4 Door Automatic” – and just watch all the matching adverts appear! It really is the easiest way to find a car that meets your criteria. 

Of course you might be thinking “what about hybrids and EV’s?” Well we haven’t forgotten them; we are just going to look at those separately so as not to ‘muddy the waters’ too much! Check out our followup Basics article ‘The Future? Less Bangs, More Humming’ for our take on the future of automotive.

About Carsnip

Carsnip is the UK’s largest used car search engine, with over 500,000 dealer sold used cars across the UK. We operate a natural language search engine, to help you find your perfect used car, and narrow down the choice by what’s most important to you.

About the Author

Sam Wardega is’s very own in house car guru and journalist.

A lifetime Petrolhead who started with Hot Wheels aged 2, and now just spends his life savings on owning his dream cars. As they say, boys don’t stop playing with toys; they just get bigger and more expensive!