Guide
Can you mix E5 and E10 petrol?
Topping up E10 with a tank of E5 super unleaded, or the other way round, is fine for almost every car. Here is the exception that matters and how to know if it is you.
It is a common moment at the pump. You usually run standard E10, but the only clear pump is E5 super unleaded, or you have half a tank of one and want to top up with the other. Can you mix them? For nearly everyone the answer is a simple yes, with one group of cars that should pay closer attention.
The short answer for modern cars
If your car is approved for E10, and every petrol car built for the UK market since 2011 is, then mixing E5 and E10 in any proportion is completely safe. They are the same petrol with a different maximum ethanol content, five percent against ten, so a tank that is part one and part the other simply ends up somewhere in between. Your engine will not notice and nothing is harmed. You can top up E10 with E5, or E5 with E10, as often as you like.
Which cars should stick to E5
The care is needed at the older end. Some classic cars, certain vehicles from the late 1990s and before, and a handful of specific models are not approved for the higher ethanol content of E10, because over time it can affect older seals, hoses and fuel lines. If yours is one of these, the advice is to use E5 super unleaded and to avoid regularly filling with E10. An occasional splash of E10 in an emergency is unlikely to cause harm, but it should not become the habit for a car that is meant to run on E5.
How to check which your car needs
You do not have to guess. The government runs a free online E10 compatibility checker where you enter your car's make, model and year and it tells you whether E10 is approved. If the checker says yes, mix and match freely. If it says no, or your car is a classic, treat E5 super unleaded as your normal fuel. When a vehicle is in any doubt, the safe default is always the lower ethanol E5.
Why E5 is also the choice for stored vehicles
There is a second reason some drivers prefer E5, beyond older engines. Ethanol attracts moisture, and fuel that sits for months in a tank can draw in enough water to cause problems. So for a classic laid up over winter, a motorbike, or garden machinery that stands idle, the lower ethanol E5 is the gentler choice for long storage, and a fuel stabiliser helps too.
The bottom line
For a normal modern car, mix E5 and E10 as freely as you like, it makes no difference worth worrying about. Save the care for older and classic vehicles, which should stick to E5, and check the government tool if you are unsure. For the fuller picture on the two grades and whether super unleaded is ever worth paying for, see our guide to E10 versus E5 petrol, and use the price finder to see which forecourts near you are cheapest today.
Common questions
Can you mix E5 and E10 petrol?
Yes, for any car approved for E10, which is every petrol car built for the UK since 2011. E5 and E10 are the same petrol with a different maximum ethanol content, so mixing them in any proportion is completely safe and your engine will not notice.
Is it bad to put E5 in a car that normally uses E10?
Not at all. E5 super unleaded is a higher octane, lower ethanol fuel and is perfectly safe in a car that normally runs E10. It simply costs more, so there is no need to use it unless the standard pump is unavailable or your handbook asks for higher octane.
Which cars should not use E10?
Some classics, many cars from the late 1990s and earlier, and a few specific models are not approved for E10, because the higher ethanol content can affect older fuel systems over time. These should use E5 super unleaded. The government's free E10 checker confirms whether your car is approved.
Does E5 petrol last longer in storage?
Yes, it is the better choice for a vehicle left standing. Ethanol attracts moisture, so the lower ethanol content of E5, ideally with a fuel stabiliser, is gentler for a classic over winter, a motorbike or garden machinery that sits idle for months.