Is a diesel cheaper to run than a petrol?

Yes, diesel engines typically use 20%-25% less fuel than their petrol equivalents. With fuel priced similarly, diesel cars can be a better buy.


When is it better to buy a diesel?

Motorists should base their decision on which type of car to buy, on their own particular needs. Deciding which type of power works best for you is essential, and it is worth spending the time to consider how you will use your vehicle.

With advanced fuel economy and efficiency, diesel cars are cheaper to run than petrol cars. They also tend to have a higher resale value, particularly larger vehicles. This makes them an ideal choice for long-distance driving.

Diesel decision tree - Is a diesel cheaper to run than a petrol?

Does diesel use less fuel?

While the gap between the fuel economy of diesel and petrol engines has been closing, the way in which diesel engines work provides an advantage that even the most sophisticated petrol engines struggle to compete with. Due to continuous improvements in technology, a diesel engine remains more fuel-efficient than similar-sized petrol engines.

While a petrol engine uses a spark to ignite a mix of air and fuel, diesel engines inject fuel into air that is heated by having been intensely compressed, where it then ignites spontaneously. The high pressures inside a diesel engine, together with the fact that it does not “throttle” the air that it draws in, creates a higher fuel efficiency.

While fuel consumption is, of course, influenced by the amount of power being produced, higher fuel efficiency means that a diesel engine will use less fuel while producing the same amount of power.


Are diesel cars better for long-distance drivers?

With this higher fuel efficiency,  diesel vehicles will usually run for longer between refuelling stops, a distinct advantage for long-distance driving.

Diesel engines are consuming less fuel while delivering the same power as their petrol alternatives.

However, when it comes to fuel, all things are not equal.  A litre of diesel fuel contains roughly 15% more energy than a litre of petrol. This means that even if the efficiency of the two engine types are the same, a diesel vehicle would go further on each tankful.

If you take into account both the energy density difference of the fuel, and the efficiency of the engine itself, that leaves the overall efficiency of the diesel engine about 20% greater than that of the petrol engine. For those motorists doing a lot of long-distance driving, this is a powerful reason to choose diesel.

The diesel engine’s higher fuel efficiency also makes diesel vehicles cheaper to run overall, which in turn impacts upon the resale value of the vehicle. Studies show that even though diesel cars often have a higher monthly lease cost than petrol cars, this is usually offset by reduced fuel costs, particularly for high-mileage drivers.

It is also worth knowing that diesel fuel costs are generally lower than petrol in most European countries, though the cost of fuel to consumers is heavily influenced by the taxation policies of national governments.

So, if you are looking for a new vehicle, and spend a lot of time on the road, diesel’s higher energy concentration and fuel efficiency makes it the best possible choice.