Petrol or diesel? Facts and quiz to help you choose

Petrol or diesel? Facts and quiz to help you choose
The petrol or diesel debate has enthused and confused drivers for decades - and has been little helped by growing air quality concerns.

However, diesel is far from dead and in some instances still remains the obvious choice for some drivers depending on a number of practical factors - not just personal preference

So what should you do?

Our in-depth guide examines the performance and driving style of both engines, along with the many cost and environmental factors associated with them to help you make the right choice – we have even included a short quiz at the end to help you decide if you are still unsure.



REMEMBER: It's worth bearing in mind news is always changing and there is often increased speculation around 'the fate of diesel'. Our guide takes into account the issues irrespective of the speculation around the fate of diesel, however, we advise checking our 'air quality' news section after reading this guide.


Performance and driving



Performance and driving

Petrol or diesel

Here we look at where you drive, how you use your car and what do you use it for to find out what type of fuel best suits your needs.

  • How do they differ in performance?

    Traditionally petrol is usually seen as a smoother drive with a sharper response and eagerness to rev, while diesels have better torque (pulling power), which makes a more relaxing drive.

    However, modern turbo-charged petrol engines offer plenty of low-down oomph, while the latest diesels respond – and sound – much like petrol engines. The clattering, agricultural diesels of old are long gone.

    Looking at the two from more of a generic point of view it can still be said that:

    • Petrol engines need to be revved to give their best, so they suit a ‘sportier’ driving style – and, by extension, a manual gearbox.
    • Diesels are best paired with the laid-back charms of an automatic ’box as generally speaking their better torque doesn’t lend itself to high revs in low gears.

    That doesn’t mean petrol engines can’t be relaxing or diesels can’t be fun, there’s still more to consider, so let’s take a deeper look into things.

  • Do you use your car for motorway driving or rural roads?

    Diesels are great on motorways, where their plentiful torque allows for swift overtaking.

    Furthermore, motorway driving will tend to rack up the miles more than anywhere else meaning you’re better off with a diesel which will often return a better MPG, more on this in the economy section below.

    Motorway driving also lends itself to the type of driving needed to maintain a diesel particulate filter - more on this in the next section.

    On the other hand, driving on rural A- and B-roads, will better suit a peppier petrol engine, which will likely offer a more rewarding driving experience and will be more suitable for quick acceleration when overtaking slower vehicles like tractors.

  • Do you more commonly drive long or short journeys?

    Enter the dreaded diesel particulate filter issue.

    Diesel particulate filters (DPFs) represent a complicated topic but, the fact remains they are a legal requirement on all diesel cars registered since 2009, meaning it cannot be ignored and adds crucial weight to whether or not you should buy a diesel car.

    The long and short of the issue is, you must regularly run a diesel engine at high speeds for between 30 and 50 minutes to allow the exhaust temperature to increase enough to cleanly ‘burn off’ the excess soot in the filter and clear it - motorway driving is ideal for this.

    Meaning for shorter journeys like to and from the shops, driving about town or if you have a shorter or slower-paced commute, a petrol engine will be more suitable.

    Diesel is also better for longer journeys because of it’s on-average increased fuel economy.

  • Country or city driving?

    It seems increasingly likely many major cities and towns will begin to use legislation to discourage diesel cars from entering them; daily charges may form part of this legislation.

    It is likely, however, that Euro 6 diesels (diesels typically (but not exclusively) registered from 1 September 2015) will be exempt from near-future charges, like they have been from the London T-charge, which came in October 2017. This has not been confirmed though.

    If most of your driving is in a city, think twice about opting for diesel. Stop-start traffic can clog diesel particulate filters (DPFs), leading to a potentially big bill for replacement.

    There is an ethical issue here, too. Older diesel engines emit higher quantities of nitrogen oxides (NOx) and microscopic particulates, which linger in the air and cause respiratory problems – a particular issue in cities, where air quality is considerably worse than in the countryside.

    Also, if most of your driving is done in the country then the muscular torque of a diesel is ideal for steep hills and tough terrain, including driving through mud or snow. Diesel engines also suit larger, heavier vehicles, such as 4x4s, which excel in such conditions.


Petrol is better for:Diesel is better for:
Short journeysMotorway driving
City drivingLong journeys
Hilly countryside driving
Towing and commercial use

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While there are many more emotive factors such as driving fun or going green: for many, this decision comes down to cost.

In this section, we examine all the costs associated with petrol and diesel cars, from the up front price of the car to insurance, tax, fuel economy, servicing costs and residual values.

Here, where we can dispel a few myths, such as diesel cars always being cheaper to run too. Calculators at the ready...

  • Initial purchase costs

    Diesel cars typically cost anything between £1,000 and £2,500 more than their petrol equivalents to buy.

    Obviously, on a supermini such as the Fiat 500, that premium represents a large chunk of the purchase price. On a luxury car such as the Mercedes-Benz E-Class, the percentage increase is more modest.

    The higher cost of diesels is partly due to the extra tech needed to get them through emissions tests. However, it’s also because buyers are prepared to pay more – in the hope of recouping costs later.

  • Insurance

    The higher purchase price of diesel cars, coupled with higher accident repair costs, can lead to increased insurance costs.

    Some experts put the uplift over petrol at between 10% and 15%. Taking the average UK car insurance premium of £484 (source: Association of British Insurers), that would mean an extra £50 - £65 annual cost.

  • Car tax

    For years, the UK car tax system incentivised diesel by basing costs on carbon dioxide (CO2) emissions.

    The most efficient diesel cars avoided VED altogether by ducking under the 100g/km barrier – something only a handful of petrol-engined cars manage.

    In April 2017, however, the car tax system changed so that only zero-emissions cars (such as electric cars) are free from tax.

    For all other cars, tax is still based on CO2 emissions, but after the first year rate is claculated, the following years will be charged at a flat rate of £140, irrespective of fuel type or emissions output.

    In April 2018: there will be another change to vehicle tax that will only affect diesels.

    It was announced in the November 2017 Autumn Budget that a first year VED supplement for diesel cars will be introduced from 1 April 2018.

    This means as of April 2018 any diesel car registered on or after this date will be treated as if it is in the tax band above for its first year of tax, unless it is a Euro 6 diesel that meets the upcoming ‘Real Driving Emissions Stage 2’ (RDE2) tests.

    This adds, for example, £20 to the first-year cost of the average diesel Ford Focus (emitting between 91-100g/km CO2) – but £410 onto the car tax price for a Land Rover Discovery (emitting between 171-190g/km CO2). The table below explains all.

    If you’re buying a second-hand car, the old tax rates still apply, meaning diesel cars will generally cost less. However, rates vary widely depending on make and model, so check our car tax comparison tables before you buy.

  • Economy

    The pump-price of a litre of petrol is usually lower, but this is outweighed by the increased efficiency of most diesel engines over petrol units of a similar output. In short, that means more miles per gallon.

    For example, the Ford Focus 1.0 Ecoboost Zetec petrol (125hp) returns 60.1mpg in official fuel economy tests, versus 74.3mpg for the Focus 1.5 TDCi Zetec (120hp). And the BMW 320i Sport petrol (184hp) ekes out 48.7mpg, compared with 68.9mpg for the 320d Sport diesel (163hp).

    This difference in economy is more pronounced in larger vehicles, such as luxury SUVs, where diesel is usually the default choice.

  • Servicing costs

    It’s a mixed picture here. Diesel engines tend to have longer servicing intervals, but their added complexity can bump up costs – particularly if a DPF replacement is needed.

    For many modern diesels, you need to add in the cost of a fuel additive, commonly known as AdBlue.

    This is used by diesel cars with selective catalytic reduction (SCR) emissions systems – most Euro 6 diesels are fitted with one. It can be a non-service item but some drivers report needing to top up the AdBlue system in between services (a warning light on the dashboard alerts them). 10 litres of AdBlue costs around £20.

    We’d think twice about buying a high-mileage diesel car outside of warranty; any savings at the pumps could quickly be wiped out by higher garage bills.

  • Residual values

    First, the good news: diesel cars that cost more to buy will usually be worth a similar percentage more when you sell. So, say you paid a £1,000 premium for a diesel, and your car holds onto 40% of its original purchase price after three years and 30,000 miles.

    That means your diesel is still worth £400 than the petrol version. In theory.

    The uncertainty over diesel means the second-hand price premium enjoyed by diesel cars could be under threat.

    There is little conclusive evidence that this is an issue at the moment, and it shouldn’t be a factor for modern diesels that meet Euro 6 emissions standards, but it is a situation worth considering as more towns and cities announce restrictions on diesel cars.

    Like all matters in the used car market, though, prices very much depend on supply and demand. Few second-hand buyers can stomach the fuel bills for a luxury saloon with a thirsty petrol engine, for instance.

  • Emissions charges

    There’s no doubt more charges affect diesel drivers, however, it’s worth remembering, currently, new Euro 6 diesels are subject to vary few of the below.

    It’s also worth noting, most of these charges are only relevant to city drivers, which petrol is more suited to anyway.

    If you are in a situation where you have a long motorway commute into a city centre, you may want to weigh up the cost of the charges you may face versus the improved fuel economy a diesel will offer on this type of commute.

    Again a Euro 6 diesel will most likely offer the best fuel economy and escape most charges, for now, but not everyone can afford a new car.

    October 2017

    £10 T-Charge introduced in Central London

    Affects: petrol and diesels

    Both petrol and diesels that do not meet at least Euro 4 standards, will face the charge and motorbikes that do not meet at least Euro 3 standards

    January 2018

    £2 parking surcharge in London Borough of Islington (council controlled parking). More boroughs are following suit with these charges

    Affects: diesels

    This charge affects all diesels, regardless of age or Euro standard

    March 2018

    Initial air quality plans published by local councils which may open the door to local charging schemes. Final plans must be published by December 2018 (TBC).

    April 2018

    Rise in first-year VED (car tax) rate on new diesels

    Affects: diesels

    This will affect non-RDE2 compliant diesel cars

    (Currently Euro 6 cars are only RDE1 compliant)

    April 2018

    Supplement in Company Car Tax rises from 3% to 4%

    Affects: diesels

    This will affect non-RDE2 compliant diesel cars

    (Currently Euro 6 cars are only RDE1 compliant)

    April 2019

    London Ultra-Low Emission Zone (ULEZ) will be launched, possibly covering a wider geographical area than the T-Charge

    Affects: petrol and diesels - but more diesel cars will be affected

    (Euro 4 is the minimum standard for petrol; Euro 6 for diesel)

    Between 2018-2020

    Glasgow, Edinburgh, Aberdeen and Dundee expected to introduce Low Emission Zones

    Affects: petrol and diesel cars - but more diesel cars will be affected

    (Euro 4 is the minimum standard for petrol; Euro 6 for diesel)


    Clean Air Zones (CAZs) anticipated in Birmingham, Nottingham, Southampton, Derby and Leeds

    Affects: petrol and diesels - but more diesel cars will be affected

    (Euro 6 is the minimum standard for diesels; Euro 4 for petrol)


    Other Scottish cities expected to introduce Low Emission Zones


    Scottish Government plans to phase out new petrol and diesel cars


    UK Government Ban on the sale of conventional diesel and petrol cars and vans

    Ones to watch

    - More UK Clean Air Zones (CAZs)

    - Government-backed scrappage scheme for trading in diesel cars

    - London-wide Euro VI standard for heavy vehicles

    - ULEZ extension to cover North and South Circular roads

    - Further increased parking charges for diesel cars

    - Increased cost of residential parking permits for diesel owners in a number of


CostsCheapest fuel type
Initial purchase costsPetrol
Insurance premiumsPetrol
Car taxEven
Servicing costsPetrol
Residual valuesDiesel

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The expression ‘do the maths’ is very apt when it comes to choosing between petrol and diesel cars.

Petrol cars are usually cheaper to buy and you’ll pay less at the pumps for a litre of unleaded. Diesel offers better fuel economy (typically 15-20mpg on a family car) and lower car tax.

Which one costs less overall depends primarily on how long you plan to keep the car.

Take the Ford Focus again. The 1.5 TDCi Zetec Edition 120 diesel costs, at the time of writing, around £700 more than the 1.0 Zetec Edition 125 petrol.

sing official fuel economy figures (60.1mpg for the petrol, 74.3mpg for the diesel) and average RAC Fuel Watch prices on 4 December 2017 (120.7p per litre for petrol, 123.1p for diesel), it would take a driver covering 10,000 miles a year almost four-and-a-half years to make back the upfront cost of the diesel in fuel savings.

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Petrol or diesel

It's not possible to provide a definitive verdict on the petrol or diesel debate, as the decision is down to the driver and how they use their vehicle. 

However, we hope the advice we have given throughout this article will help you make an informed decision.

It is important to look at all of the criteria above and carefully consider what your driving needs are and how you are going to use your vehicle before making your purchase.

It is also important too, not to be bullied into buying petrol by the media's perceived ‘war on diesel’.

While the air quality debate is well worth factoring in, it is still advisable to weigh up all of your options, looking at all of the above factors without any preconceptions of what you should drive, before you choose to buy.

As a general rule of thumb, when buying small, mid-size cars or sports cars most people opt for a petrol engine, and when buying large cars and SUVs most people opt for a diesel as each engine is generally speaking better suited to these types of cars.

However, with the development of modern technology such as hybrid and plug-in hybrid electric vehicles, much depends on the specific make and model of the car and the range of other factors we looked into above. It is more important than ever to carefully consider the type of driving you do and get expert advice before making a choice.

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