Even with the rising popularity of electric and hybrid models, diesel and petrol cars still make up the biggest proportion of vehicles on the roads in the UK today.

When comparing petrol and diesel cars, you should consider multiple things, including your budget, annual mileage and where and how you drive your car.

Both types of cars offer numerous benefits as well as some drawbacks. But which is right for you and should you buy a diesel or petrol car? In this guide, we’ll go over the key differences of each, pointing out the scenarios where you may benefit from one over the other.

How do petrol and diesel engines differ?

Both diesel and petrol engines are what is known as an internal combustion engine. In these engines, fuel is combined with oxygen in a small space. This combustion process produces the energy to power your car.

In petrol engines, fuel is compressed with air before being ignited by a spark plug. However, in a diesel engine, the air is compressed first within the combustion chamber and then the fuel is introduced by injection.

These differences mean that petrol cars have a relatively low compression ratio which produces lower amounts of power at a higher fuel consumption rate. On the other hand, diesel engines have a high compression ratio which produces more power at a relatively low fuel consumption rate.

Petrol vs diesel cars comparison

Purchase price

When comparing the initial purchase price of both diesel and petrol cars, diesels typically cost more, even on the used market. This is mainly because modern diesel cars are fitted with complex engine technology.

To reduce particulate emissions, newer diesels are fitted with a selective catalytic reduction (SCR) system, which costs more to produce. Also, because diesel engines use a higher compression ratio, the engines have to be built to withstand this process. This requires the use of heavier materials, which can often come at more of a cost.

The price you pay will also be dependent on other things such as the car’s age, make and model. For example, purchasing a used diesel can be cheaper than purchasing a new petrol car and you can sometimes find a higher-spec car at a comparative price.

Fuel efficiency

When comparing like for like, you will get a better mile per gallon (mpg) from a diesel car. This is because diesel fuel produces more energy compared to petrol. This makes diesel better suited for long-distance journeys, whereas petrol cars are more suited for short trips.

Fuel price

You will notice at the pumps that diesel typically costs more than petrol. This is mainly due to the differences in formulation. Diesel is inherently more complex to formulate because of its higher energy density and combustion requirements. Additional additives and processes are required to produce diesel which drives up the costs to produce it.

The price you pay at the pump for petrol and diesel also fluctuates according to supply and demand. As demand increases, so does the price of the fuel.

This is why you should consider how and where you drive. Although diesel appears more costly than petrol at the fuel pump, it can be a more economical option for those who cover longer distances.


Maintenance costs will depend on the particular make, model and age of the car as well as the mileage, and how it is driven.

Modern diesels are fitted with more complex parts. These often come at a higher cost when they need replacing. For example, if a diesel particulate filter (DPF) needs replacing, this can set you back anywhere between £1,000 to £3,500. Therefore, if you are looking to buy a used diesel car, this is something that you should enquire about before you make a purchase.

On the other hand, while petrol cars can be cheaper to repair, they often wear more quickly than their diesel alternatives. So although they may be cheaper to repair, they may mean more frequent trips to the garage over their lifespan which could ultimately end up costing you more in the long run.

Resale value

When comparing both diesel and petrol, diesel cars are typically more expensive to buy. This is because their engines often require extra parts compared to petrol vehicles.

Much like the initial purchase price, When considering the resale value, in some cases, diesels actually hold their value better than petrol cars. This is particularly true for large diesels with petrol alternatives as the petrol option can often be costly to run.

Noise and comfort

Due to the difference in engine structure and technology, petrol engines are usually quieter than diesel. They often provide a smoother driving experience with a sharper response to acceleration.

On the other hand, diesel engines produce a higher level of torque which can make for a more relaxing drive. Diesel engines can also be noisier compared to their petrol alternatives. Although, they have become a lot more refined over the years so newer diesels have less of a noticeable engine noise compared to petrol engines.

Engine lifespan

Diesel and petrol engines are built differently to handle the different combustion requirements. Because diesel engines have a higher compression ratio they are often built to be more robust. Furthermore, the composition of diesel helps to lubricate parts of the engine when in use, which can help further prolong the life of the engine further.

Towing capacity

If you regularly tow a large trailer, caravan or horse box, then a diesel is a more practical solution. Diesel engines naturally generate more torque, which is what’s needed to comfortably tow heavy loads.

Environmental impact

There is a lot of debate and misinformation out there about the environmental impact of diesel and petrol cars.

Diesel cars are often vilified, with many believing that they are worse for the environment than petrol cars. Whilst this is partly true, diesel cars do emit less hydrocarbons, carbon monoxide, lead pollution and other particulates compared to their petrol counterparts. However, they do emit more noxious gases and significantly more particulates which contributes to poor air quality – particularly amongst older diesel engines. It’s worth noting that modern diesel engines are far superior in terms of emissions.

Whilst petrol cars do not emit as much nitrogen oxide (NOx) gases as older types of diesel, they do emit more carbon dioxide (CO2) which is a key contributor to greenhouse gases.

Diesel vs petrol pros and cons

Diesel Pros:

More efficient for long journeys
Strong performance on motorways
Better suited for towing heavy loads
Lower CO2 emissions

Diesel Cons:

Less efficient on short journeys
Can be more costly to buy
Produces more particulate emissions
Potentially higher servicing and maintenance costs

Petrol Pros:

More efficient for short journeys
Lower purchase cost
Cheaper fuel at the pumps
Produce less particulate emissions
Potentially lower servicing and maintenance costs

Petrol Cons:

Less efficient on long journeys
Higher fuel consumption
Higher CO2 emissions
Not suited for towing heavy loads

Should I buy a diesel or petrol car?

The answer to this question mainly depends on your lifestyle, the type of driving you do and how many miles you typically cover.

If you frequently drive longer distances, regularly travel on a motorway or need to tow heavy loads, then a diesel may be more suitable. However, if your journeys are shorter and you generally travel fewer miles, then a petrol may be more suitable.

Should I buy a petrol or diesel car if buying second hand?

For some, purchasing a used diesel or petrol car can be a more viable option than buying a brand-new one. As new cars can depreciate more quickly, buying second-hand can save you a significant amount of money. You may also find, that your budget will allow you to get a higher-spec car at a much more affordable price compared to buying brand new.

For more guidance on buying a used petrol or diesel car, check out our used car buying checklist.

Frequently Asked Questions