Fuel Types
E10 vs Unleaded 91: Compatibility and Cost per km
Australian E10 vs U91 guide: check vehicle compatibility, compare octane and fuel economy, and calculate the exact break-even discount per litre.
Key points
Key takeaways
Use E10 only when the vehicle manufacturer approves ethanol-blended petrol and the bowser meets the car's minimum octane rating.
Australian government guidance says E10 can use about 3% more fuel on average, but your car and driving conditions determine the actual difference.
There is no universal cents-per-litre break-even rule: the required discount rises and falls with the U91 price and your measured fuel-use penalty.
Compare current E10 and U91 prices for the same area, then calculate cost per 100km rather than choosing from the bowser price alone.
Prices near you
Compare local E10 and U91 prices
Search a suburb or postcode to open the map with the cheaper reported E10 or U91 grade identified at each station.
- Map selection
- E10/U91 compares the cheaper reported grade at each station and identifies which fuel supplied that price.
- Final check
- Check the grade, update time and bowser price, then use the guide's formula with your own fuel economy.
Search suburb or postcode
Search opens the local map with E10/U91 selected. Open the Australia-wide comparison.
Using this guide
Before you act on the guide
Check the station price, report time and distance before changing your route.
Short answer: compatibility first, then cost per kilometre
Choose between E10 and Unleaded 91 (U91) in two steps. First, confirm that the vehicle manufacturer allows E10 and that the fuel meets the car's minimum Research Octane Number (RON). Second, compare the two fuels by cost per 100km using current local pump prices and the car's actual fuel use. A cheaper litre is not automatically a cheaper kilometre.
E10 vs Unleaded 91: what is different?
| Check | E10 | Unleaded 91 |
|---|---|---|
| Fuel definition | Unleaded petrol containing up to 10% ethanol | Regular unleaded petrol sold as 91 RON |
| Vehicle suitability | Vehicle-specific; the manufacturer must approve ethanol-blended petrol | Suitable only when the manufacturer permits 91 RON petrol |
| Fuel use | Government guidance uses about 3% higher consumption as an average comparison | Baseline for this calculation |
| Octane | Often marketed as 94 RON, but check the bowser label | 91 RON |
| Value test | Compare cost per 100km with the same local area, report time and driving conditions | |
Can your car use E10?
Do not decide from the build year alone. The ACCC says most new and some older models can use E10, but some new vehicles and many pre-1986 vehicles cannot. Check the fuel-flap label, owner's manual or manufacturer website for both ethanol compatibility and minimum RON.
The NSW E10 checker has an important limit: its database generally includes petrol vehicles made after 2000 only where manufacturer information is available. A missing result is not approval to use E10; ask the manufacturer.
A car can be ethanol-compatible and still require premium petrol. If the handbook specifies a minimum of 95 or 98 RON, neither U91 nor the commonly sold 94 RON E10 in this comparison meets that requirement. Follow the minimum rating on the vehicle, not the colour or marketing name on the pump.
Is every Australian E10 fuel 94 RON?
No national rule makes the word “E10” a promise of 94 RON. The Australian Government defines E10 by ethanol content: petrol sold in Australia may contain up to 10% ethanol, and ethanol-blended petrol must be labelled. Many E10 products are marketed as 94 RON, but the current NSW FuelCheck fuel guide notes an E10 product that is only guaranteed as 91 RON. Read the bowser's RON label before filling.
The transparent break-even formula
NSW Government E10 guidance says E10 has about 3% less energy than the equivalent amount of U91 and can increase fuel consumption by about 3% on average. Treat 3% as a starting assumption, not a promise about one car.
Cost per 100km = litres per 100km × price in dollars per litre.
Break-even E10 price = U91 price ÷ (1 + E10 fuel-use penalty).
If the assumed penalty is 3%, divide the U91 price by 1.03. E10 is cheaper per kilometre only when its pump price is below that result.
Worked example: U91 at 180c/L
Assume the car uses 8.00L/100km on U91 and 3% more fuel on E10.
- U91 cost: 8.00 × $1.80 = $14.40 per 100km.
- Estimated E10 use: 8.00 × 1.03 = 8.24L/100km.
- At 175c/L, E10 cost: 8.24 × $1.75 = $14.42 per 100km.
- Exact break-even E10 price: 180 ÷ 1.03 = 174.76c/L.
In this example, E10 needs to be about 5.24c/L cheaper than U91. The old idea that 4c/L is always enough fails because the break-even gap changes with the U91 price.
| U91 price | Break-even E10 price at 3% more fuel use | Required discount |
|---|---|---|
| 160c/L | 155.3c/L | 4.7c/L |
| 180c/L | 174.8c/L | 5.2c/L |
| 200c/L | 194.2c/L | 5.8c/L |
| 220c/L | 213.6c/L | 6.4c/L |
A 3% fuel-use penalty therefore requires E10 to be about 2.91% cheaper at the pump. If your measured penalty is 1%, 2% or 4%, replace 0.03 in the formula with 0.01, 0.02 or 0.04.
Use your own fuel records for a better answer
Compare several full-tank intervals for each fuel under similar driving conditions. For each interval, calculate litres added ÷ kilometres travelled × 100. Average the E10 results and the U91 results, then calculate the penalty as (E10 L/100km ÷ U91 L/100km) − 1. Use that result in the break-even formula. Weather, traffic, tyre pressure, air conditioning and driving style can otherwise overwhelm a small fuel difference.
Cars, boats and other engines
If the manufacturer approves both E10 and U91, the Queensland Government says it is acceptable to switch between them. For motorcycles, mowers, generators and other small engines, use the equipment maker's instructions rather than the passenger-car rule. Transport for NSW generally does not recommend ethanol-blended petrol for boats because of water contamination and fuel-system concerns.
Compare local E10 and U91 prices
The gap changes by service station, suburb and report time. Use the local comparison on this page to open the map with E10/U91 selected, then check the winning fuel grade, reported price and update time at each station. Put the reported prices shown into the formula before choosing a fuel.
Source notes
Compatibility and fuel facts were checked against the Australian Competition and Consumer Commission, the Australian Government fuel-quality regulator, NSW Government E10 guidance and FAQs, Queensland Government E10 guidance, and Transport for NSW marine advice. Sources last checked 20 July 2026.
Common questions
Frequently asked questions
Only when the pump discount is larger than the car's fuel-use penalty. Divide the U91 price by 1 plus the penalty. With a 3% penalty and U91 at 180c/L, E10 must cost no more than about 174.8c/L to break even.