Stand at an Australian bowser and you're offered a menu: E10, 91, 95, 98, sometimes E85 or "premium diesel". The price gaps between them look small per litre — but multiplied over a year of driving, picking the wrong fuel quietly costs hundreds of dollars. Picking the right one takes about five minutes of understanding, once.
Here's the menu decoded.
First, what the numbers actually mean
The number on the pump is the fuel's RON — Research Octane Number. Octane isn't "power" or "quality"; it measures how much compression the fuel tolerates before it ignites on its own (knocking or "pinging").
| Fuel | Octane (RON) | What it is | Who it's for |
|---|---|---|---|
| E10 | ~94 | Regular unleaded blended with up to 10% ethanol | Most petrol cars roughly 2000s onwards — check compatibility first |
| 91 | 91 | Standard unleaded | Any petrol car whose manual says "91 or higher" |
| 95 | 95 | Premium unleaded | Cars whose manual requires or recommends 95 |
| 98 | 98 | High-octane premium | Cars whose manual requires 98; performance/turbo engines |
The golden rule sits in your glovebox: your owner's manual states a minimum octane. Below it, never go. Above it, you're usually just donating money — more on that below.
E10 vs 91: the break-even maths
E10 is regular unleaded with up to 10% ethanol. Two facts drive the decision:
- Ethanol raises octane — E10 is around 94 RON, so it more than covers a "91-minimum" engine.
- Ethanol contains less energy than petrol. E10 has roughly 3% lower energy content, which in practice means slightly higher fuel consumption to travel the same distance.
So E10 is only genuinely cheaper when its per-litre discount beats the consumption penalty. The break-even rule of thumb:
E10 needs to be at least ~3% cheaper than 91 to save you money.
As a purely illustrative example: say 91 is 190¢/L. Three percent of that is about 6¢. If E10 is only 3–4¢/L cheaper — a common spread — the "cheap" fuel is costing you more per kilometre. If it's 8¢ cheaper, E10 wins. The right answer changes station to station and week to week, which is why it pays to compare your two fuels, not just glance at the big number on the board.
Can your car take E10?
Most petrol cars sold in Australia since the mid-2000s are E10-compatible, but "most" isn't "yours". Check before you switch:
- The NSW Government's E10 compatibility checker (nsw.gov.au) lets you look up your make and model.
- The FCAI (the carmakers' industry body) publishes the underlying compatibility list (fcai.com.au).
- Or simply read the fuel-filler flap and owner's manual.
Older vehicles, some imports, motorcycles and small engines (mowers, outboards) often shouldn't use ethanol blends at all.
Is 95 or 98 worth the premium?
The distinction that matters is "required" versus "recommended" in your manual:
- Required 95/98: no decision to make. Using 91 in an engine that requires 95+ risks knock and long-term damage; modern engines will pull timing to protect themselves, costing you power and economy anyway.
- Recommended 95/98 (minimum 91): the engine can exploit the higher octane with a little more power or efficiency. Whether that's worth 15–25¢/L extra is genuinely marginal — for most commuting, the economy gain doesn't repay the price gap.
- Minimum 91, and you're buying 98 "as a treat": this is the expensive myth. A standard engine designed for 91 cannot extract meaningful benefit from 98-octane fuel — it simply doesn't have the compression or tuning to use it. Octane is not a cleaning product or a power additive; premium fuels' detergent packages differ only modestly from regular's.
If your manual says 91, the cheapest way to look after your engine is a reputable station and the right fuel — not a more expensive number.
The one-paragraph decision guide
- Manual says 98 required → 98, always.
- Manual says 95 required → 95 or 98, whichever is cheaper per litre that day.
- Manual says 91 minimum and your car is E10-compatible → E10 when it's at least ~3% cheaper than 91, otherwise 91.
- Not E10-compatible → 91.
- Premium "for the engine's sake" on a 91-spec car → skip it.
Compare your fuel, not the headline price
Station price boards advertise one grade; the spreads between E10, 91, 95 and 98 differ surprisingly between stations. FuelWise shows live per-grade prices for every station around you — pulled from official government feeds like NSW FuelCheck — so you can compare the fuel your car takes, see whether today's E10 discount actually clears the 3% bar, and stack your loyalty discounts on top. Set your fuel type once and the map, the cheapest-station badge and the buy-or-wait forecast all speak your grade.