What E10 is
E10 is regular unleaded petrol blended with up to 10% ethanol, which in Australia is mostly made from sugar cane by-products and grain. It is sold widely in New South Wales and Queensland, where governments have encouraged it, and less in the other states. Its octane rating is about 94, higher than regular 91 unleaded.
Ethanol contains roughly a third less energy per litre than petrol. At 10% of the blend, that makes E10 about 3% less energy-dense than regular unleaded, and most cars use about that much more of it to cover the same distance. Results vary by car and driving, from barely measurable to a little more than 3%.
The break-even discount
If E10 costs you 3% more litres, it only saves money when it is more than about 3% cheaper per litre. That 3% is a percentage of the price, so the break-even discount grows as fuel gets dearer.
| Price of 91 unleaded | E10 must be cheaper by at least |
|---|---|
| 160c a litre | 4.7c |
| 200c a litre | 5.8c |
| 250c a litre | 7.3c |
| 300c a litre | 8.7c |
Assumes the car uses 3% more E10 than 91 for the same distance. The break-even discount is the 91 price × 3 ÷ 103.
When petrol was $1.60, a 4 or 5c discount on E10 made it worth buying. At $2.50 the same discount means you are paying slightly more per kilometre.
If you want to know your own car's penalty, fill up with each fuel two or three times and compare the kilometres per tank on similar driving. Then put your numbers in below.
Is E10 cheaper for your car?
Can your car use it?
Most petrol cars sold in Australia in the past two decades are approved for E10, but not all, and many older cars, motorcycles, boats and small engines are not. Check the label inside the fuel flap or the owner's manual, or the E10 compatibility list from the Federal Chamber of Automotive Industries. If your car is approved, E10 will not harm it.
Premium 95 and 98
Premium unleaded has a higher octane rating, which lets high-compression and turbocharged engines run more advanced ignition timing without knocking. If your manufacturer specifies 95 or 98, use it. On 91 the engine will retard its timing and you will lose power and economy, and possibly more.
If your car is designed for 91, premium is a different question. Modern engines designed for 91 cannot make much use of the extra octane, and for most drivers any gain in economy is far smaller than the extra that premium costs at the pump, which is usually well over 10c a litre. Some premium fuels also carry more detergent additives, which is a reasonable reason to use one occasionally, not every week.
What to do
- If your car needs premium, buy premium, and compare premium prices between servos rather than with 91.
- If your car can use E10, buy whichever of E10 and 91 is cheaper per kilometre. At current prices that means E10 only when it is around 7c or more cheaper than 91.
- Either way, the servo and the day you buy make a far bigger difference than the grade. The gap between the top and bottom of a price cycle is often four or five times the gap between E10 and 91.
Where these figures come from
Wholesale prices are the terminal gate prices published each weekday by the Australian Institute of Petroleum, which we hold back to 2004. The national figure is AIP's own average where it has published one, and our weighted calculation in between, which matches AIP's to within 0.1c. Oil and currency prices are delayed market closes. Excise rates are the ATO's. We check every figure against that data before publishing and correct mistakes in the update log. Spotted one? Email hello@thepetrolprice.com.