Australian motorists face a common dilemma at the bowser: should they choose E10 or regular 91 unleaded petrol? With E10 typically priced 3-5 cents per litre cheaper, it seems like an obvious choice.
But the reality is more nuanced than simple price comparisons suggest. This article examines the data behind both fuels to help you make an informed decision.
Understanding the Basics
- E10 Fuel: A blend of up to 10% ethanol and 90% regular unleaded petrol, with an octane rating of 94 RON (Research Octane Number) in Australia.
- 91 Unleaded: Standard unleaded petrol with no ethanol content and an octane rating of 91 RON.
The key difference many Australians miss is that E10 actually has a higher octane rating than regular 91 unleaded, not the same rating as commonly believed.
Octane Rating: What It Actually Means
Octane rating measures a fuel’s resistance to engine knock (premature detonation). Higher octane fuel can withstand more compression before igniting, which allows engines to operate more efficiently under high load.
- E10: 94 RON – Better knock resistance
- 91 Unleaded: 91 RON – Standard knock resistance
For context, premium unleaded petrol in Australia is typically 95-98 RON.
Does Higher Octane Mean More Power?
Not automatically. Higher octane fuel only provides more power if your engine is designed to take advantage of it through:
- Higher compression ratios
- Advanced ignition timing
- Turbocharging or supercharging
Most standard Australian vehicles are designed for 91 RON minimum. Using E10’s 94 RON in these engines may provide marginal benefits, but won’t transform performance.
Energy Density: The E10 Trade-off
Here’s where the picture gets complicated. While E10 has a higher octane rating, it contains less energy per litre than pure petrol.
Energy Content Comparison:
- Pure petrol: ~34.2 MJ/L (megajoules per litre)
- Ethanol: ~24 MJ/L (approximately 30% less energy)
- E10 blend: ~33 MJ/L (roughly 3.5% less than pure petrol)
This means that theoretically, you need about 3-4% more E10 to travel the same distance as regular 91 unleaded.
Real-World Fuel Economy Data
Studies and consumer reports show varied results:
- RACV testing has indicated fuel consumption increases of 1-3% when using E10 compared to regular unleaded
- NRMA data suggests some vehicles show negligible difference in fuel economy
- Individual experiences vary widely based on driving style, vehicle type, and engine management systems
The fuel economy penalty is generally smaller in practice than the theoretical 3.5% because:
- Modern engine management systems can optimize for ethanol content
- The higher octane may allow for more efficient combustion timing
- Driving conditions and style matter more than small fuel differences
Price Analysis: Does E10 Save You Money?
Let’s run the numbers with typical Australian fuel prices (January 2025):
Scenario 1: 50-litre tank
- E10 at $1.75/L: $87.50 total
- 91 at $1.80/L: $90.00 total
- Upfront savings: $2.50
But accounting for fuel economy: If E10 delivers 2% less fuel economy:
- E10: 50L gets you 490km (assuming 500km on 91)
- Cost per km: $0.1786
- 91: 50L gets you 500km
- Cost per km: $0.1800
Real savings: $0.14 per 100km, or about $0.70 over a full 500km tank.
Break-even calculation: E10 needs to be at least 2-3 cents cheaper per litre to offset the fuel economy penalty for most drivers.
Engine Compatibility: Can Your Car Use E10?
This is crucial. Not all vehicles are E10-compatible.
Generally Compatible:
- Most petrol vehicles manufactured after 2000
- All vehicles manufactured after 2010
- Modern motorcycles (check manufacturer specifications)
Often Incompatible:
- Pre-2000 vehicles, especially pre-1986
- Some high-performance European vehicles
- Older motorcycles and small engines
- Some marine engines and power equipment
- Classic and vintage cars
Why the incompatibility? Ethanol is a solvent that can:
- Degrade rubber and plastic fuel system components in older vehicles
- Attract moisture, leading to corrosion
- Cause fuel system blockages in vehicles not designed for it
Always check your vehicle’s owner manual or the fuel filler cap for E10 compatibility. The Federal Chamber of Automotive Industries maintains a compatibility list at fcai.com.au.
Environmental Considerations
E10 is marketed as a more environmentally friendly option, but the data is mixed.
Potential Benefits:
- Ethanol is derived from renewable sources (primarily sugarcane in Australia)
- Can reduce net CO2 emissions by 1-3% compared to pure petrol
- Reduces dependence on fossil fuels
Complications:
- Land use and water consumption for ethanol crop production
- Energy used in ethanol production and transportation
- The overall carbon benefit depends heavily on production methods
- Increased fuel consumption partially offsets emission benefits
Research from CSIRO suggests that Australian ethanol from sugarcane offers better environmental credentials than corn-based ethanol used in other countries, with greenhouse gas emission reductions of approximately 60-65% compared to fossil fuel production.
Performance Testing: Acceleration and Power
Limited independent testing in Australia has examined actual performance differences:
Dynamometer Testing Results:
- Peak power differences: Typically within 1-2%, often within margin of error
- Torque curves: Virtually identical for engines designed for 91 RON minimum
- Acceleration (0-100 km/h): Differences of 0.1-0.2 seconds at most
The verdict: For everyday driving in standard vehicles, performance differences are imperceptible. The higher octane of E10 doesn’t translate to meaningful power gains in engines not designed for premium fuel.
Regional Availability and Market Trends
E10 availability varies significantly across Australia:
Strong E10 Markets:
- NSW: Mandated 6% ethanol blend across the state’s fuel supply
- Queensland: Good availability, strong government support
- ACT: Readily available
Limited E10 Markets:
- Victoria: Patchy availability, less popular
- South Australia: Limited stations
- Western Australia: Minimal presence
- Tasmania and NT: Very limited
This regional variation affects both pricing and consumer choice.
Expert Recommendations
When to Choose E10:
- Your vehicle is E10-compatible (post-2000, confirmed by manufacturer)
- E10 is at least 2-3 cents cheaper than 91 unleaded
- You support renewable fuel initiatives
- You drive a standard commuter vehicle with normal performance requirements
When to Choose 91 Unleaded:
- Your vehicle is older or not confirmed E10-compatible
- Price difference is minimal (less than 2 cents/litre)
- You prioritize maximum fuel economy
- You store fuel for extended periods (ethanol attracts moisture)
- You’re fueling motorcycles, marine engines, or small equipment
When to Skip Both:
- Your vehicle requires or recommends 95+ octane fuel
- You drive a high-performance or luxury vehicle
- Your owner’s manual specifies premium fuel
Common Myths Debunked
- Myth 1: “E10 damages all engines” False. Modern vehicles are designed for E10. Incompatibility is primarily an issue for older vehicles.
- Myth 2: “E10 provides the same performance as 91” Partially false. E10 has higher octane (94 vs 91) but lower energy content, resulting in roughly equivalent real-world performance.
- Myth 3: “E10 is always cheaper in the long run” False. It depends on the price difference and your vehicle’s fuel economy with each fuel type.
- Myth 4: “Higher octane always means better performance” False. Higher octane only benefits engines designed to use it. Using 94 RON in an engine designed for 91 RON provides minimal benefit.
The Conclusive Trade Off
E10 and 91 unleaded represent a trade-off rather than a clear winner:
E10 Advantages:
- Higher octane rating (94 vs 91 RON)
- Typically lower price per litre
- Renewable content with environmental benefits
- Suitable for most modern vehicles
E10 Disadvantages:
- 2-3% lower fuel economy
- Incompatible with many older vehicles
- Not suitable for long-term fuel storage
- Limited availability in some regions
91 Unleaded Advantages:
- Higher energy density
- Universal compatibility with petrol engines
- Consistent quality and availability
- Better for fuel storage
91 Unleaded Disadvantages:
- Lower octane rating
- Typically more expensive per litre
- Entirely fossil fuel-based
For most Australian drivers with compatible vehicles made after 2000, E10 offers modest savings when priced appropriately (2-3+ cents cheaper). However, the difference is marginal enough that convenience, availability, and personal preference are equally valid decision factors.
The most important advice: check your vehicle’s compatibility, do the math based on local prices, and don’t stress too much about the choice. The difference in real-world costs and performance is smaller than most people think.
