E10 vs E5 Petrol: The Complete Guide to Which Fuel You Should Use

What are E10 and E5?

E10 and E5 are the two grades of unleaded petrol you will see at UK fuel stations, and the letters and numbers tell you exactly what is in them. The “E” stands for ethanol, a renewable alcohol made from plant materials like wheat, corn, and sugar beet. The number is the maximum percentage of ethanol blended into the petrol.

E5contains up to 5% ethanol mixed with 95% unleaded petrol. This was the standard unleaded fuel across the UK until September 2021. It is still available today, typically marketed as “Super Unleaded” or “Premium Unleaded” with an octane rating of 97 or higher.

E10 contains up to 10% ethanol mixed with 90% unleaded petrol. It became the standard unleaded fuel in the UK from September 2021 onwards, carries an octane rating of 95, and is clearly labelled at every pump to prevent accidental use in incompatible vehicles.

Why was E10 introduced?

The UK government introduced E10 as part of its strategy to cut transport carbon emissions. Increasing the ethanol content reduces reliance on fossil fuels and lowers overall CO2. The government estimates that the switch from E5 to E10 cuts UK transport CO2 by around 750,000 tonnes per year, equivalent to taking 350,000 cars off the road.

The change supports the broader net-zero target and the planned 2030 ban on new petrol and diesel car sales. Most petrol stations across Europe have adopted the higher ethanol blend as part of a wider EU initiative to improve air quality and reduce greenhouse gas emissions.

Is your car compatible with E10?

This is the most important question. Using E10 in a car that was not designed for it can cause damage over time, because ethanol is more corrosive to certain rubber seals, fuel pump components, and fuel lines than pure petrol.

The good news: roughly 95% of petrol cars on UK roads can safely use E10. Almost every car manufactured after 2011 is compatible. Cars built between 2000 and 2011 are usually compatible too, but worth checking. Cars from before 2000 should be treated with caution and verified before any E10 goes in the tank.

Around 600,000 vehicles on UK roads cannot safely use E10. These are typically classic cars, vintage vehicles, and some specialist models from the early 2000s. If yours is one of them, stick with E5 Super Unleaded.

To check, consult your vehicle handbook or use the UK Government's official E10 compatibility checker. You can search by registration or by make, model, and year. Some manufacturers, including Mercedes-Benz, also publish their own model-by-model E10 compatibility tools.

Cost and fuel economy

E10 is generally cheaper than E5 at the pump, typically by 10p to 15p per litre, with E10 being the lower-priced option. As of 2026, the average price gap is around 2.9% in E10's favour.

Ethanol carries slightly less energy per litre than pure petrol, so E10 returns slightly lower fuel economy than E5. The UK government quotes a difference of around 1%, with some independent tests suggesting up to 2%. On a typical 400-mile tank that is roughly 4 to 8 fewer miles. Most drivers will not notice it.

Even after accounting for the small efficiency hit, E10 still works out cheaper overall for cars that can use it. A 15p-per-litre saving comfortably outweighs a 1% drop in mpg, so unless you have a specific reason to choose E5, E10 is the cheaper choice.

Performance, octane, and engine characteristics

For most modern vehicles there is no noticeable performance difference between E10 and E5. You will not feel a change in how the car handles, accelerates, or drives.

E10 has an octane rating of 95, while E5 reaches 97 or higher. Octane measures resistance to knocking under combustion. If your handbook specifies 95 octane, E10 standard unleaded is the right fuel. If it specifies 97 or higher, E5 Super Unleaded is what your engine wants. Some high-performance engines designed for premium fuel will run more cleanly on E5, but for normal driving the real-world difference is negligible.

For older vehicles, the bigger issue is corrosion. Cars made before 2011 often had fuel system components that were not designed for higher ethanol content. Prolonged use of E10 in those cars can degrade rubber seals, fuel pumps, and fuel lines. This is why the 2011 cutoff matters; it is not about performance, it is about what the fuel system can tolerate over years of use.

Storage, mixing, and common worries

Mixing E5 and E10 is safe in any E10-compatible car. The blended fuel sits somewhere between 5% and 10% ethanol depending on the ratio, and a modern engine handles it without complaint. You do not need to drain your tank if you accidentally fill up with the wrong grade once.

A single tank of E10 in an incompatible car is not an emergency. You may notice slightly rougher running, but a single tank will not cause immediate damage. Use E5 Super Unleaded for the next fill and carry on as normal. The problems come from prolonged repeated use of E10 in vehicles that were not designed for it.

Storage matters for cars that sit unused. E10 is less stable than E5 because ethanol is hygroscopic; it absorbs moisture from the air. If a vehicle sits for months with E10 in the tank, the ethanol can absorb water that separates out of the fuel, causing starting issues and potentially rust inside the fuel system. For everyday cars this never matters because the fuel gets used long before any meaningful water absorption. For classic cars, second cars, caravans, and seasonal motorbikes, E5 is the safer fuel; alternatively a fuel stabiliser additive will protect E10 in long-term storage.

At the pump, the standard unleaded handle (usually green) is E10. The Super Unleaded or Premium Unleaded pump is E5. Every UK forecourt is required by law to offer at least one E5 grade fuel, so you will always be able to find E5 if your car needs it.