Fuel Types & Quality
Super Unleaded
Can you mix unleaded and super unleaded?
CheckFuelPrices Editorial
Expert Written • 4 industry sources
Yes, you can safely mix unleaded (E10) and super unleaded (E5) in the same tank. Both are petrol grades that meet UK fuel quality standards and are fully compatible with each other — topping up with one when the other is already in your tank will not harm your engine.
Why Mixing Is Safe
Same base fuel:
Both unleaded (E10) and super unleaded (E5) are petrol grades regulated under the same British Standard (BS EN 228). They share the same base chemistry and mix without any adverse reaction.
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Different octane ratings, not incompatible fuels:
The key difference is octane rating — standard unleaded is 95 RON, super unleaded is typically 97–99 RON. Mixing them simply produces a blend somewhere between the two octane levels.
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Ethanol content difference is minor:
E10 contains up to 10% ethanol and E5 up to 5%. Mixing them creates a mid-level ethanol blend that is safe for all E10-compatible vehicles.
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What Actually Changes When You Mix
Blended octane rating:
Mixing equal parts 95 RON and 97 RON fuel gives roughly 96 RON in the tank. Your engine's ECU will adapt automatically — no action needed.
Performance benefit is diluted:
If you use super unleaded for its higher octane performance benefit, adding standard unleaded will partially reduce that advantage depending on the ratio in the tank.
No engine warning lights or damage:
Modern engines are designed to handle variations in fuel grade. Mixing will not trigger warning lights or cause any mechanical damage.
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When You Might Mix in Practice
E10-incompatible vehicles:
If your car requires E5 (pre-2002 vehicles or certain classics), super unleaded is the recommended grade as it remains E5. Accidentally mixing in some E10 is unlikely to cause immediate damage, but minimising E10 use is advised.
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Emergency top-up:
If you run low and the only pump available is a different grade to what is already in your tank, filling up is always safe — mixing is far better than running out.
Finding the Cheapest Super Unleaded Near You
Price gap varies by station:
Super unleaded typically costs 10–20p per litre more than standard unleaded, but the gap varies considerably between stations and regions.
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Compare live prices before you fill:
CheckFuelPrices shows live super unleaded and unleaded prices at 4,000+ UK stations, updated every 30 minutes, so you can find the best price near you.
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Sources
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