Petrol vs Diesel: Which Is The Better Fuel?

Petrol and diesel are the two main fuels that we use to power our cars and the technology inside of them. They're integral when it comes to powering the engine technology that keeps up moving. Both have their obvious pros and cons, but which one should you choose if you’ve about to start leasing a car?

I’ve created a small guide with the pros and cons of petrol and diesel to help you decide.

What is petrol?

Fuels don’t come more ‘fossil’ than petrol. Petrol comes from petroleum – the chemical remains of fossilised sea animals and plants from millions of years ago.

As these forms of life died and sank to the bottom of the sea, they were covered by tonnes of sand and silt. Over time, intense pressure and heat turned the remains into fossils, broke them down into hydrocarbons, and then formed oil-saturated rock.

Petroleum (whose names comes from a combination of the Latin, “petra” meaning rock, and “oleum” meaning oil) is a liquid hydrocarbon that’s extracted from these layers of rock. This crude oil is then fractionally distilled (ie. separated into its constituent parts) from which we’re able to get petrol and diesel.

What is diesel?

Diesel is a type of distilled petroleum, extracted from crude oil.

It’s a dirty, heavy fuel, found lower down in the distillation spectrum but the higher boiling points of the fuel means that diesel engines can offer better thermodynamic performance and fuel efficiency than petrol engines.  

Which is best for fuel efficiency?

The figure to pay attention if you’re trying to work out which is best in terms of fuel efficiency is MPG – the amount of miles that the car will do on one gallon of fuel – and when it comes to that, diesel is the stand out winner. Using about 17% less fuel than petrol, it’s a better choice if you like getting your value for money.

Make the most of that fuel efficiency while it lasts though. The Government has decreed that the sale of all new diesel powered cars will be banned by 2040.

  • Winner: Diesel

Which is most affordable?

It’s a fact that petrol is cheaper at the pump. It’s also a fact that petrol cars are much cheaper to maintain than diesel cars. But although petrol might be cheaper it certainly doesn’t go as far as diesel in terms of mileage and power.

Diesel is more expensive but you can get more mileage out it, meaning that you need to fill up your car less. It’s pretty much a draw for affordability if you’re comparing the two.

You really need to decide which you were prefer: lower cost, but more frequent, fill-ups with petrol, or higher cost, less frequent fill-ups with diesel.

  • Winner: Draw (Petrol works out cheaper in the short-term, but diesel is better in the longer term.)

Which is best for the environment?

Let’s not lie to ourselves, both petrol and diesel are pretty damaging to the environment.

But that said, diesel is a heavier, dirtier fuel than petrol because of the fact that it’s unrefined, making it more damaging on the environment. Diesel creates some pretty nasty nitrogen oxide and nitrogen dioxide fumes which can be really damaging on our health.

Petrol is by no means squeaky clean though, so don’t be burning tanks of it like there’s no tomorrow.

Years ago lead used to be added to petrol to reduce knocking noises in the engine. Although it got rid of the knocking sound, it also caused a massive spike in lead pollution in the air – pollution that went on to cause an increase in respiratory disorders, cancers and development problems in infants. Thankfully it was banned in 2000 and all the petrol now sold in the UK is unleaded.

  • Winner: Petrol (But only marginally.)

Best for availability

Both petrol and diesel are readily available at any service station or roadside garage that wants to stay in business.

You’ll usually get different options of petrol and diesel there too with premium versions like Shell V Power and BP Ultimate which are slightly more refined and are supposed to deliver performance and efficiency benefits.

  • Winner: Draw