Guide
What Is RON? Octane Ratings Explained
Every petrol pump in Australia is labelled with a number — 91, 95, 98. That number is the fuel's RON, and understanding it takes the guesswork out of choosing fuel. Here's what octane actually measures, and what it doesn't.
What does RON stand for?
RON stands for Research Octane Number. Australian petrol is sold and labelled by its RON — 91, 94 (E10), 95 and 98 are the ratings you'll see on the board.
What does octane actually measure?
Octane measures a fuel's resistance to knock — its ability to withstand compression in the cylinder without igniting on its own before the spark plug fires. Higher octane = more resistance to that premature, uncontrolled combustion (known as "knocking" or "pinging").
Crucially, octane is not a measure of how much energy or power a fuel contains. A higher-RON fuel doesn't hold more energy per litre; it simply tolerates higher compression before it self-ignites.
Does higher octane mean more power?
Not by itself. Higher octane only helps in engines designed to use it — high-compression, turbocharged, or performance engines that run timing and compression a regular engine can't. In those, premium fuel lets the engine work as intended, which can mean more power and better economy.
In an ordinary engine designed for 91, pouring in 98 doesn't add power or energy — the engine can't take advantage of the extra knock resistance, so you mostly just pay more. See Is premium fuel worth it?.
What are the octane ratings in Australia?
| Fuel | RON | Notes |
|---|---|---|
| Regular unleaded (91) | 91 | The everyday standard |
| E10 | ~94 | Ethanol blend, higher octane than 91 — see E10 explained |
| Premium unleaded (95) | 95 | Premium unleaded (PULP) |
| Premium (98) | 98 | Highest octane commonly sold |
Is octane the same as diesel's cetane?
No. Diesel isn't rated by octane at all — it uses the cetane number, which measures how readily diesel ignites under compression (diesel engines rely on compression ignition, not spark). Octane and cetane describe opposite qualities, which is one reason petrol and diesel are never interchangeable. See Diesel prices Australia.
Which octane should I use?
Use the minimum RON your manufacturer specifies — printed inside the fuel filler flap or in the owner's manual. Going below it risks knock and engine damage; going above it rarely helps unless the engine is built for it. Full guidance: Which fuel for my car?.
Related: Which fuel for my car? · Premium fuel — 95 vs 98 · E10 fuel explained
Compare every octane's price near you — download Petrol Australia for iPhone and Android at petrolaustralia.com.au.