Petrol and diesel are the most commonly used types of fuel in the world. This is thanks primarily to their versatility and simplicity, as well as the hard work of a long line of great thinkers who have improved, evolved and adapted the Internal Combustion Engine.

Despite their shared success and crude oil origin, in practice they perform very differently. To understand this difference, it is first important to show where they come from, and how they become their own unique fuels.

After Crude Oil is extracted from the Earth’s “Oil window”, a term given to the only area of the Earth’s crust where oil is able to form, the substance is transported to refineries. The job of these refineries is simple – turn relatively worthless crude oil into one of many refined products including fuels, lubricating oils, waxes, asphalt, petrochemicals and pipeline quality natural gas.

Petrol and diesel begin their individual journeys during a process called fractional distillation, where crude oil is heated and certain products are separated depending on their boiling point. During this, petrol is created between 35 degrees to 200 degrees and diesel is produced between 250 and 350 degrees – a fact which explains why, in its final form, diesel is much less flammable than petrol.

Beyond this, the fuels go through a few more processes which see additives and elements blended in to make them commercially acceptable. This is especially important for diesel fuel, where detergent additives are needed to deal with the increased level of soot and combustion by-product being left in the engine.

With the additives included, the two fuels are ready for sale – bar some premium alternatives who receive a few more tweaks.

Keeping in mind that diesel and petrol engines, the way they work, and how they have changed in the past twenty years makes judging the pros and cons of each fuel difficult, here is a quick explanation of what makes them unique.

Starting with diesel; the most important and most talked about benefit is the increase in fuel efficiency and economy over petrol. Being quite a dense fuel, in that it weighs more and has higher energy density, it achieves the same effect as petrol all the while using approximately 30% less fuel.

On top of this, diesel cars come with a host of other advantages because of the nature of the  fuel: their engines are built more ruggedly and so last longer, the fuel produce 20% less carbon emissions than petrol, and –importantly for trucks and off-roaders – modern diesels harness the fuel’s improved torque and so are much better at towing things.

Petrol, the long time commercial favourite, has much less going for it than it once did. As diesel technology has improved, petrol has started to lose its golden lead – but it still offers a few unique assurances. Being a more refined fuel and needing a lighter engine to run it, petrol cars are generally much easier to drive, are much quieter and feel more responsive when compared to their diesel counterparts.

But perhaps the most striking advantage petrol has is its price, and the price of cars that use it. Diesel models usually have a premium of about $2000 dollars.

This premium is important too, as the historic advantage petrol has had over diesel at the pump may be a thing of the past. Whilst it isn’t uncommon to see diesel selling for more at the local petrol station, the latest data provided by the Australian Institute of Petroleum shows that the national average for diesel is 120 cents per litre, and the national average for petrol is 121 cents per litre.

But even with the full set of benefits before you, it is impossible to say whether one fuel is superior. Rather, they both have advantages and perform better in certain circumstances. Sitting down, and thinking about the type of driving you do, for how long, and to what end, is the best way to decide whether petrol or diesel will work best for you.

– Connor Pound