Guide
E10 vs E5 petrol: which should you use?
E10 is the standard green pump and the cheaper choice for almost every modern car. Here is when the pricier E5 super unleaded is worth it, and when it is just marketing.
Since September 2021 the standard petrol on UK forecourts has been E10, and the older E5 has moved up to the super unleaded pump at a premium price. Most drivers pour in the cheaper green one without a second thought, which is usually right. But it is worth knowing what you are buying, whether your car minds, and whether the dearer stuff ever earns its extra pennies.
What the numbers actually mean
The E stands for ethanol, the plant based alcohol blended into petrol to cut carbon emissions. E10 contains up to ten percent ethanol. E5 contains up to five percent. That is the whole difference. E10 is the standard grade you find on every forecourt. E5 is now sold mainly as super unleaded, the 97 or 99 octane pump, at a noticeable premium.
Will E10 harm your car?
For almost everyone, no. Every petrol car built for the UK market since 2011 is approved for E10, and the vast majority built since the early 2000s are fine too. If your car is newer than about fifteen years old, you can use E10 without a moment of worry.
The exceptions are older and classic vehicles, some cars from the late 1990s and before, certain mopeds and a handful of specific models, where the higher ethanol content can affect seals, hoses and fuel lines over time. If you are unsure, the government runs a free E10 compatibility checker where you enter your make, model and year. When in doubt on an older vehicle, use E5 super unleaded, which stays widely available precisely for this reason.
Does E10 cost more to run?
This is the part that surprises people. E10 is the cheaper fuel to buy, but ethanol carries slightly less energy than petrol, so a tank of E10 takes you a touch fewer miles than the same tank of E5 would. The drop is small, on the order of one to two percent for most cars. In real driving that is the difference between, say, 45 miles per gallon and around 44.
Put the two effects together and the maths still favours E10 for ordinary cars. The pump saving of several pence a litre comfortably outweighs the tiny loss in economy. You would need to be chasing a very specific edge case for E5 to work out cheaper per mile in a car that does not require it.
When is super unleaded worth paying for?
There are three honest reasons to buy E5 super unleaded, and one bad one.
Your handbook requires it. Some high performance and prestige engines are designed for higher octane fuel and say so in the manual. Follow the manual. This is the one case where the premium is not optional.
You drive an older or classic car. As above, the lower ethanol content is gentler on older fuel systems, and E5 is the safer long term choice.
You are storing a vehicle over winter. Ethanol attracts water, which can cause problems in a tank left standing for months, so E5 is often preferred for seasonal classics, motorbikes and garden machinery.
The bad reason is the belief that super unleaded makes an ordinary modern car noticeably quicker or cleaner. For an engine designed to run on standard petrol, the gain is usually too small to feel and never enough to justify the price. The premium fuels differ mainly in their additive packages, not in any magic your engine can use. If you want to spend less per mile, the reliable move is to buy standard E10 at a competitive forecourt, not premium fuel at any forecourt.
The bottom line
For the great majority of drivers, standard E10 is the correct and cheaper choice. Check your car if it is older than about fifteen years or a classic, and reach for E5 super unleaded only when the handbook demands it or the vehicle is older or being stored. Then focus on the thing that dwarfs the E10 versus E5 question entirely, which is the price of the forecourt you pull into. Put your postcode into the price finder to see who near you is cheapest today.
Common questions
Is E10 petrol bad for my car?
For almost all cars, no. Every petrol car built for the UK since 2011 is approved for E10, and most built since the early 2000s are fine. The exceptions are some classics and older vehicles, where E5 super unleaded is the safer choice. The government runs a free E10 compatibility checker if you are unsure.
Does E10 give worse fuel economy than E5?
Slightly. Ethanol holds a little less energy than petrol, so E10 gives roughly one to two percent fewer miles per tank than E5. For most cars that is a drop of about one mile per gallon, which the lower pump price of E10 more than makes up for.
Is E5 super unleaded worth the extra money?
Only in specific cases: when your handbook requires higher octane fuel, when you drive an older or classic car, or when you are storing a vehicle over winter. For an ordinary modern car, super unleaded gives no gain you would notice and is not worth the premium.
What is the difference between E10 and E5 petrol?
The number is the maximum percentage of ethanol in the fuel. E10 has up to ten percent and is the standard, cheaper grade. E5 has up to five percent and is now sold mainly as super unleaded at a premium. That ethanol content is the only meaningful difference.