unleaded 91 or e10 Page 5

Short answer: use whatever your owner’s manual and fuel flap allow; if it says E10 is fine, it usually is. E10 is up to 10% ethanol and typically about 94 RON in Australia, while regular unleaded is 91 RON; E10 often costs a tad less but returns about 2–3% worse fuel economy. If your car requires 95 or 98 RON, or isn’t rated for ethanol, skip E10 and stick to the specified premium or 91 as directed. Older vehicles and small engines (mowers, boats) can be fussy, so don’t play chemist—check the handbook. For most modern cars approved for it, E10 vs 91 is a wallet-and-range wash, with a slight nod to E10 when it’s notably cheaper per litre.