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Which petrol should you use?

Learn all about the different types of fuel and the best petrol to fill your car with.

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Ben Gribbin

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When you pull up at a servo, do you ever find yourself confused by all the different fuels on sale? Surely petrol is petrol, right? Well, not exactly. This guide will help you understand all you need to know about picking the right gasoline.

Tl;DR! I'm at the pump!
Look at the sticker on the inside of your filler cap. Or check your manual for the minimum RON level petrol you can use in your car.

How to understand the various types of petrol on sale in Australia

In Australia, there are several variants of petrol commonly sold at service stations. Each formulation is labelled with a number, which denotes its octane rating or Research Octane Number (RON).

Warning! It's incredibly important that you use the correct petrol to suit your car's engine! It's even more important you don't put diesel in by accident.

Most people mistakenly believe the higher the number, the more powerful or energy-dense the fuel. That's not the case. The number indicates how resistant that particular petrol concoction is to a phenomenon known as engine knock, or in really simple terms, the ability of the engine to govern the timing of when the fuel ignites.

Unleaded 91 RON Petrol

91 RON Unleaded Petrol

91 RON is your basic, standard fuel. It's also the cheapest, non-ethanol containing petrol.

Which cars can I use Unleaded 91 in?

Most petrol cars built after 1986 are compatible with 91 RON unless otherwise stated. If your owner's manual or fuel flap sticker stipulates 91RON, you can use higher octane fuels – though the promises of improved fuel economy and performance may not be appreciable in real-world driving. If you have a car that requires leaded fuel (a classic car for example), you'll need to add a leaded petrol replacement additive or substitute into the tank. You can also have a mechanic retrofit tougher parts to handle the lead-free petrol. You may also decide to use a higher octane fuel for a vintage car.

91 Ron brand names

  • Regular Unleaded
  • Unleaded 91
  • Unleaded Petrol
  • Special Unleaded 91
95 RON Premium Petrol

95 RON Unleaded Petrol

The first of the "Premium" kinds of petrol, is 95 RON. The increased number of octanes means manufacturers can use different technologies and higher levels of compression to extract optimal efficiency from smaller engines, all without inducing engine knock.

Which cars can I use 95 RON in?
Examples of petrol cars that require 95 RON fuel as a minimum include the Volkswagen Polo, Nissan Patrol, Alfa Romeo Stelvio and the Ford Focus. 95 RON is the standard used widely throughout Europe, so that's why you see a lot of imported vehicles use higher octane petrol. Cars that require 91 RON petrol will run happily on 95 and should alter ignition timing to adapt automatically (if they have electronic fuel injection). This could bring slight emissions and economy benefits, though real-world results will vary depending on your car and the conditions you drive in.

95 Ron brand names

  • Unleaded 95
  • Caltex Vortex Premium 95
  • Premium Unleaded 95
  • Premium 95
  • Extra 95
98 RON Premium Unleaded

98 RON Unleaded Petrol

This fuel is generally a minimum requirement for high-end/performance vehicles, it's also the most expensive petrol.

Which cars can I use 98 RON in?

Typically luxury/high-end/performance petrol cars. For example, the Audi RS5 drinks 98 RON as a minimum.

98 Ron brand names

  • BP Ultimate Unleaded 98
  • Supreme+ 98
  • Shell V-Power Unleaded 98
  • Unleaded 98
  • Premium Unleaded 98
  • Vortex Premium 98 Unleaded
E10 Ethanol Petrol

Ethanol E10

Ethanol E10 is just ordinary unleaded petrol (91 RON) with up to 10% ethanol, a type of clear alcohol. Ethanol often is made from the waste products, making it a renewable (depending on the source) and also non-fossil fuel based ingredient. Ethanol contains up to 35% oxygen, which can actually help your engine burn cleaner. While cheaper, E10 contains approximately 3% less energy than unleaded RON 91 petrol.

Which cars can use Ethanol E10?

Check your vehicle's ethanol compatibility online. You shouldn't use E10 in cars that have carburettors (as opposed to fuel injection) and high-performance models.

E10 Ethanol brand names

  • Caltex Bio E10 Unleaded
  • E10 Unleaded Petrol
  • Special E10 94
  • Shell Unleaded E10
  • BP Unleaded 91 (with up to 10% renewable ethanol)
E85 Petrol

E85

E85 has a fuel blend of 70-85% ethanol to 15% petrol. RON measures 105 (this figure varies with the seasons). Availability is quite limited. It is possible to convert existing cars to use E85. It offers better internal engine cooling. V8 Supercars are powered by E85, since the introduction of the fuel in 2009.

Which cars can use Ethanol E85?

Only vehicles specially modified to run on E85 are compatible.

Engine knock

Knocking occurs when the fuel/air mixture within the engine begins to combust before (or in a place other than) it's designed to. This knocking is generally audible, making your engine sound rough, like a bag of spanners and irregular. Knock is sometimes called pinging.

Engine knock will cause damage to internal components. It can cause small pits to form on the surface of precisely machined parts. Because the air/fuel mixture is off, you won't get as complete a combustion, which results in the formation of sooty, carbon deposits. These further compound the problem, resulting in poor running.

It is possible that knocking can lead to a total engine failure, due to the premature breakdown of multiple parts like seals and metal engine components. These bits are exposed to the overheating and stresses outside of the engine's design specifications, caused by the pressures of knocking.

This video from spark plug manufacturer NGK demonstrates the regular combustion process and knocking. Engine knock starts at 0:59.

Average NSW petrol prices December 2019

FuelAverage Price in NSW
Unleaded 91201.4 cents
Ethanol 94 (E10)200.6 cents
Premium 95217.5 cents
Premium 98224.4 cents

*Figures from NSW Fuel Check

Frequently asked questions about petrol types

Can I use a higher RON fuel than recommended?

Yes, you can put a higher RON fuel into your car, for example, 98RON into a 91RON minimum car. You may or may not experience better efficiency from your engine. Fuel producers list possible benefits of higher octane fuels as:

  • Better engine responsiveness
  • Higher engine efficiency
  • Fuel economy gains
  • Emission improvements

I've accidentally put a lower octane fuel in. What should I do?

If you put 91RON petrol into a high-performance car that is designed for 98RON premium fuel, you should read your owner's manual or contact the manufacturer first before starting the engine. Newer cars will likely auto adjust ignition timing thanks to a knock sensor and you may be ok to run the car, topping up with premium fuel to compensate. However, you do run the risk of possibly damaging internal components. Engineers from major car companies say it's risky, so it's best to pay attention at the pumps and follow the guidance on your fuel cap sticker, rather than make a mistake. Older cars can't re-tune on-the-fly.If you decide to use the car, listen out for new and unusual pinging noises, like metallic pops. If you hear this, the engine is suffering from knocking. If you're really worried, there are fuel additives on sale that can boost fuel octane levels.

Help! I've put the wrong fuel in my car! What do I do now?

If you put diesel into a petrol vehicle or vice versa, do not start the engine! You'll need to contact a misfuelling service. They'll have to drain the fuel tank and flush your fuel lines to prevent catastrophic (and costly) damage.

Can I use E10 Ethanol?

First, you need to check whether your car is compatible with Ethanol fuel. The Federal Chamber of Automotive Industries (FCAI) has a guide on whether your car can run Ethanol blend unleaded petrol.

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Picture: Getty Images and supplied

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Ben Gribbin is an experienced automotive writer and life-long car enthusiast with a passion for restoring classic vehicles. He brings many years of experience working with and writing about cars to Finder. See full bio

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