Fuel Types & Quality E5 vs E10

Can you mix E5 and E10 petrol?

CheckFuelPrices Editorial Expert Written • 4 industry sources

Reviewed by Jonathan Mathews VERIFIED

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Yes, you can safely mix E5 and E10 petrol in the same tank. Both are grades of unleaded petrol and are fully compatible with one another — mixing them simply results in a blend with an ethanol content somewhere between 5% and 10%.

What E5 and E10 Actually Are

E10 is the UK standard: E10 became the standard grade of unleaded petrol at UK forecourts in September 2021. It contains up to 10% renewable ethanol, blended with regular petrol. 2

E5 is now the premium grade: E5, which contains up to 5% ethanol, is still available at most stations but is now sold as the higher-octane 'Super Unleaded' grade, typically 97–99 RON. 2

Only the ethanol content differs: Both grades use the same base petrol and meet UK fuel quality standards. The sole meaningful difference is how much ethanol is blended in. 3

Is Mixing Them Safe?

Completely safe to mix: Mixing E5 and E10 in your tank causes no harm to your engine or fuel system. The result is simply a mid-blend with an ethanol percentage between 5% and 10%. 4

No immediate action needed: If you accidentally filled with E10 when you normally use E5 (or vice versa), there is no need to drain the tank — just use the fuel as normal. 3

Incompatible vehicles are the exception: A small number of older or classic vehicles are not E10 compatible, meaning they should avoid E10 altogether rather than dilute it by mixing. Use the Government's E10 compatibility checker if unsure. 2

When You Might Choose One Over the Other

E10 is cheaper: Because E5 is sold as Super Unleaded, it typically costs 10–15p per litre more than E10 standard unleaded. For most drivers, E10 is the economical choice. 1

E5 suits performance or classic cars: If your vehicle manufacturer recommends 97+ RON, or your car pre-dates widespread E10 compatibility, E5 Super Unleaded remains the better option regardless of mixing. 4

Finding the Right Fuel at the Right Price

Prices vary station to station: Both E10 and E5 Super Unleaded prices differ significantly across stations in the same area. Checking before you fill up can save several pounds per tank. 1

CheckFuelPrices shows both grades: CheckFuelPrices lists live petrol prices updated every 30 minutes at 4,000+ UK stations, so you can quickly find who has the cheapest E10 or E5 near you. 1