Since September 2021, standard unleaded petrol at UK forecourts has been E10. The older E5 grade is still sold as a "super" premium option. Here's what the numbers after the "E" mean, and which one your car should be using.
What the "E" number means
The "E" stands for ethanol — a renewable biofuel blended into petrol to cut carbon emissions. The number is the maximum percentage of ethanol in the blend:
- E10 contains up to 10% ethanol. It is now the standard 95-octane unleaded at almost every UK forecourt.
- E5 contains up to 5% ethanol. It is sold as a higher-octane "super unleaded" (97–99 octane) and usually costs noticeably more per litre.
The switch to E10 was a government move to reduce transport emissions — blending more ethanol into the national fuel supply was estimated to cut CO₂ by roughly the equivalent of taking hundreds of thousands of cars off the road.
Can my car use E10?
The vast majority of petrol cars can. Every new petrol car sold in the UK since 2011 is approved for E10, and most built since the late 1990s are fine too. However, some older and classic vehicles, certain motorbikes, and a handful of specific models are not compatible, because ethanol can degrade some older rubber seals, plastics and metals over time.
The government runs a free online E10 compatibility checker where you enter your make, model and year. If your vehicle isn't compatible, you should keep using E5 super unleaded — the higher ethanol content of E10 could cause damage with prolonged use. Using E10 once by mistake in an incompatible car won't wreck the engine, but it shouldn't become a habit.
Does E10 affect fuel economy?
Slightly. Ethanol carries less energy per litre than petrol, so E10 delivers marginally fewer miles per gallon than E5 — typically around 1% fewer. For most drivers that difference is too small to notice at the pump, and it's far outweighed by the price gap: E5 super unleaded is often 10–20p a litre dearer than E10. Unless your car specifically requires high-octane fuel, paying extra for E5 rarely makes financial sense.
When premium (E5) petrol is worth it
Some high-performance and sports engines are designed to run on higher-octane fuel and may run better on E5 super unleaded. If your owner's manual specifies a minimum octane rating of 97 or higher, use E5. For an ordinary family car, the standard E10 is what the manufacturer intended and the cheaper choice.
The bottom line
For nearly all modern cars, E10 is the right and cheaper choice. Only use E5 super unleaded if your vehicle is older and incompatible with E10, or if the manufacturer specifically requires high-octane fuel. If you're unsure, check your car against the government's E10 compatibility tool before filling up.