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Petrol: What does it all mean?

By Samantha Stevens, 01 Sep 2015 Car Advice

Explaining petrol from premium fuel to RON

It’s often hard to justify spending that extra dime on a premium fuel. But is it worth it, and does it make a difference? We answer your burning questions on petrol fuels and sort the facts from the fallacies.

Are more expensive fuels simply burning up your dollars as well as the octane, or could you burn through an engine if you scrimp at the bowser? To answer these questions we need to turn to RON – no, not a bloke called Ron.

We are talking about a fuel’s Research Octane Number. Put simply: the higher the RON, the more expensive the fuel. Some cars need a premium fuel, others don’t.

Is it best to pump 98RON into your 1985 Honda Civic to get more kilometres and reduce engine wear and tear? Or is this a foolish fallacy?


Petrol engines work on compression and ignition. In short, fuel and air are forced into each cylinder and compressed before the spark plug ignites the mixture. The result: an explosion of energy, or power. Essentially, the higher the compression of the engine, the more power it can develop.

Now, a RON rating is how much compression a fuel can handle before it ignites. Higher octane fuels can handle more compression; therefore they have a higher RON rating. This makes them perfect for performance engines.


Most turbocharged and supercharged performance engines – and even some small-capacity engines (one-litre or three-cylinder) – have a requirement to run on premium fuel, at a minimum. Preferably, however, ultra-premium fuel with a 98 RON rating or above should be used.

These engines are built and then tuned to run on the highest-octane fuel and will produce more power from it as a result.

It’s not only about getting the right power and performance from the juice – not running on the recommended fuel can be harmful to the engine, causing pre-detonation or ‘knock’.

To avoid the fuel from igniting in the cylinders from compression alone, instead of from the spark, the fuel must be able to handle the pressure, as 98+ RON fuel does.

Ultra-premium fuels can go right up to 102 RON (and even further), but typically to get the best out of the fuel and to find more performance, the car has to be tuned by a specialist.

On the flipside, running a car on ultra-premium fuel when it isn’t tuned for it produces negligible results. Marketing may tell you that premium fuel will give you more kilometres and a longer living engine – which may be true in the (very, very) long run – but ultimately you’re probably only paying for the feel-good factor.


The middle-of-the-pack fuel that is 95 RON, or premium unleaded (PULP), is both your safest bet and most affordable exercise when it comes to the choice at the bowser.

This isn’t to say that ultra-premium fuels aren’t worth the extra coin, but if your car has a requirement for 95RON and above – and you aren’t running turbos or pushing it hard in any way – then there may be no need for ultra-premium.

Many European cars run on 95RON because it is the standard fuel in the EU and it’s the fuel they are tuned to run on.

Keep reading if you have an older car.


Unleaded petrol (ULP) has a RON rating of 91, and cars which require premium fuel (the warning is usually on a sticker on your fuel filler cap) are usually pretty happy to chug away on this fuel.

However, it’s getting difficult to find straight 91RON fuel these days, as most unleaded options at the bowser are actually E10.

E10 fuel is an ethanol blend of 90 per cent unleaded and 10 per cent ethanol. Ethanol is a biofuel additive – bio in that it is a somewhat sustainable resource with its roots in sugar cane, wheat, corn, and even potatoes and household wastes. It’s also a cheaper proposition, as the excise on it is subsidised by the government.

But there are several catches to this ‘cheaper’ fuel. Firstly, Ethanol may burn cooler, but it also burns faster – a car’s consumption of E10 can be up to four per cent higher per litre than ULP.

Secondly, older cars don’t like the stuff. If your car is older than 1986, then it’s premium (PULP) fuel for you. Most post-1986 vehicles can handle E10 fuel, however it’s best to consult your handbook to ensure the fuel is suitable for your car. Or jump on the Federal Chamber of Automotive Industries website: www.fcai.com.au/environment/can-my-vehicle-operate-on-ethanol-blend-petrol


Where E10 is 10 per cent ethanol, E85 is, of course, 85 per cent ethanol and only 15 per cent unleaded fuel. This fuel is strictly for vehicles tuned to it, and carries a high RON rating (as high as 108). It burns faster but cooler, and good power can be pulled from it. This makes it popular for performance vehicles and track-day cars, but it has floundered in the mainstream commercial market.

Bio-fuel vehicles such as the Holden Commodore saw little take up, and the Flex-Fuel Commodore has quietly bowed out of the market this year after a short shelf life.

The availability of the fuel was the key problem, despite these vehicles being able to run on premium petrol or even E10 as well as E85.

Like many fuel and energy alternatives, it is yet to make it to mainstream acceptance.

Looks like good ol’ fossil fuels will be around for a few years yet.