E10 vs E5 petrol: which should you buy?
The difference between E10 unleaded and E5 super unleaded, which cars can use E10, and whether premium petrol is worth the extra.
Since September 2021 the standard unleaded at UK pumps has been E10, petrol blended with up to 10% renewable ethanol. The older E5 blend, with up to 5% ethanol, is still sold as super unleaded.
What the numbers mean
The figure is the maximum share of bioethanol in the fuel. Ethanol is made from crops such as wheat and sugar beet, and blending more of it cuts the fossil carbon in each litre. Both grades meet the same British standard, and both are 95 octane or higher.
Can my car use E10?
Almost every petrol car built since 2011 can use E10, and many older cars can too. Some classic cars and older mopeds are not compatible, because ethanol can damage seals and fuel lines over time. The government has a free E10 compatibility checker; use it if your car was built before 2011.
If you fill an incompatible car with E10 by mistake, you do not need to drain the tank. Top up with E5 next time and avoid repeating it.
How much more does E5 cost?
Right now the UK average for E10 is 167.7p and for super unleaded 186.4p, a gap of about 18.7p a litre. On a 50 litre fill that is roughly £9.35 extra.
Is super unleaded worth it?
For most cars, no. Engines designed for 95 octane will not gain power or economy from 97 or 99 octane fuel. Performance cars that specify 98 octane in the handbook are the exception, as are cars that are not E10 compatible. E10 also contains slightly less energy per litre, so a small drop in miles per gallon (around 1%) is normal.