Fuel 
Stand at the bowser and you've got a choice: 91, 95 or 98. The numbers go up, the price goes up, and the marketing tells you the dearer one is "premium". So it must be better, right? Not necessarily. For most ordinary cars, paying for 98 buys you almost nothing - you're handing over an extra 10 to 15 cents a litre for a benefit your engine can't use.
But that's not the whole story. Some cars genuinely need premium, and running 91 in them is a false economy that can cost you more in the long run. This guide explains what those octane numbers actually mean, why higher isn't automatically better, and exactly how to work out which fuel your car wants. If you just want to see the price gap near you right now, pull it up on the live Fuel Daddy map - free, no sign-up.
What do 91, 95 and 98 actually mean?
Those numbers are the RON - Research Octane Number. RON measures one specific thing: how resistant the fuel is to igniting under pressure before the spark plug fires. That's it. A higher number means the fuel can handle more compression without detonating early. It is not a measure of how much energy, power or "cleaning" the fuel contains.
This is the single most misunderstood fact about petrol, so it's worth saying plainly: higher octane does not mean more energy or more power for most cars. 91 and 98 carry roughly the same energy per litre. Octane is about knock resistance, not grunt. A higher number only helps if your engine is designed to take advantage of it.
Does higher octane give you more power?
Only if your engine is built for it - and most aren't. Modern engines use a sensor called a knock sensor that listens for early detonation and pulls timing back when it hears it. A high-compression or turbocharged engine can advance its timing on 98 and make a little more power. A garden-variety naturally aspirated engine tuned for 91 has nothing extra to give; the spare octane just goes along for the ride.
So when someone says "I put 98 in and it felt smoother," there are two possibilities. Either their car actually benefits (it's a premium-required engine), or it's the placebo of having just filled the tank. For a 2015 Corolla or a base-model hatch, pouring in 98 is like buying race tyres for a trip to the shops - the capability is real, but your car can't use it.
91 vs 95 vs 98: the quick comparison
Here's how the three grades stack up. Note the key column - who it's actually for - matters far more than the octane number itself:
| Grade | RON (octane) | Typical price gap | Who it's for |
|---|---|---|---|
| 91 (Regular Unleaded) | 91 | Baseline | The vast majority of Australian cars. If your manual says "91 minimum", this is all you need. |
| 95 (Premium) | 95 | ~5–10 c/L over 91 | Cars that specify 95 minimum - many European models, some turbos. |
| 98 (Premium Plus) | 98 | ~10–15 c/L over 91 | High-performance, high-compression and many turbo engines that specify 95/98. |
Worth knowing: 91 and E10 sit at the cheaper end, and for the E10-versus-91 question specifically (which is a different debate to octane), our E10 vs Unleaded 91 guide breaks it down. Drivers weighing petrol against the other pump entirely should read diesel vs petrol.
Does the better economy of 98 cancel out the price?
This is where the maths usually kills the case for premium. The rough rule of thumb is about 1% better fuel economy per octane number when an engine can use it - so 98 over 91 might, at best, deliver around 2–3% better economy in a car tuned for it. The problem is the price gap is bigger than that.
Say 91 is 180 c/L and 98 is 195 c/L. That's an 8.3% price premium for, at most, a 2–3% economy gain - and that's only if your car can actually exploit the higher octane. In a car designed for 91, the economy gain is roughly zero. You're paying 8% more for nothing. The numbers simply don't work unless your engine requires the higher grade. Want to run it for your own car and driving? Plug your figures into the Fuel Daddy fuel cost calculator.
So which cars genuinely need premium?
A real minority - but it's a real one. Your car probably needs 95 or 98 if it's:
- Turbocharged or supercharged. Forced induction raises cylinder pressure, which raises the risk of knock. Many turbo engines specify 95 minimum.
- A higher-compression or performance engine. Hot hatches, sports cars and a lot of performance variants are tuned around premium.
- Many European models. A good chunk of VW, Audi, BMW, Mercedes and Mini engines specify 95 minimum from the factory.
If your car requires (not just "recommends") premium and you feed it 91, the knock sensor protects the engine by retarding timing - you lose power and economy, and you can end up spending more per kilometre than if you'd just bought the right fuel. In a premium-required car, 91 is the false economy, not 98.
What about the "premium cleans your engine" claim?
This one isn't pure marketing - but it's oversold. Most premium fuels do carry a heavier dose of detergent additives than the cheapest 91, and those additives help keep injectors and intake valves clean over time. That's a genuine, if modest, benefit. The honest catch is that all petrol sold in Australia must meet a minimum additive standard, so 91 isn't running your engine dirty.
If you've got an older engine, or one you suspect has carbon build-up, an occasional tank of premium for its detergent package is a reasonable, cheap bit of insurance. But buying 98 every fill purely "to clean the engine" in a car that runs fine on 91 is paying a steep ongoing premium for a small, slow benefit. A periodic tank does most of the work.
How do I check the minimum octane for my car?
Don't guess - check, because getting it wrong costs you money in both directions. There are three reliable places to find your car's minimum octane:
- The inside of the fuel flap. Many cars print the minimum RON right there (e.g. "Unleaded 91 minimum" or "Premium 95 only"). Open the flap and look first.
- The owner's manual. Look up "fuel" or "fuel requirements". It will state a minimum and note whether higher octane is required or merely recommended.
- The manufacturer's specs online. A quick search for your make, model and year plus "minimum octane" will usually confirm it.
Watch the wording. "Required" or "minimum 95" means you must use that grade. "Recommended" or "91 minimum, 95 for best performance" means 91 is safe - the higher grade is optional. If it says 91 minimum, you can stop reading: buy the cheapest 91 or E10 you can find and pocket the difference.
The bottom line
For most cars on Australian roads, 98 is a waste of money - you're paying 10 to 15 cents a litre for octane your engine was never built to use. Octane is about knock resistance, not power or energy, so unless your manufacturer requires a higher grade, regular 91 (or E10) does the job for less. The smart move isn't "always buy premium" or "always buy cheap" - it's buy what your car's fuel flap tells you to, then find it for the lowest price.
If your car requires 95 or 98, don't skimp - running 91 in it is the genuine false economy. For everyone else, save the premium and put it toward something useful. Either way, once you know your grade, compare prices across every nearby servo on the live fuel map before you fill up.
