E5 fuel type is petrol that contains up to 5% ethanol. It is usually sold as super unleaded. E10, by comparison, contains up to 10% ethanol and became the standard grade for unleaded fuel in September 2021.
That is why many drivers now compare E10 vs E5. For most newer petrol cars, E10 is suitable. But some classic cars and older petrol vehicles may be better suited to E5 because its lower ethanol content is often gentler on older fuel-system components.
This matters because ethanol is hygroscopic, meaning it pulls moisture from the air into your fuel tank. In older cars, this water-ethanol mix can become acidic, corroding metal tanks and 'eating' through non-ethanol-resistant rubber hoses and gaskets. In simple terms, E5 is often the safer choice for older petrol cars, while E10 is the normal option for most modern ones.
This guide explains what E5 is, how it compares with E10, and how to work out which fuel makes sense for your car.
What is E5 Petrol? Explained: Composition, Octane & Key Features
E5 petrol is a type of unleaded fuel that contains up to 5% ethanol and at least 95% petrol. Its lower ethanol blend is the main thing that sets it apart. In practice, this means it is often seen as the gentler option for some older engines and parts within the fuel system.
At most petrol stations, E5 is usually sold as super unleaded or premium unleaded rather than as the standard pump option. It also tends to have a higher octane rating than regular petrol, often around 97 to 99 RON.
The key features of E5 are simple:
- lower ethanol content
- higher octane
- better suitability for cars that may not do as well with fuel that contains more ethanol.
That is why some drivers choose it for older cars, performance models, or vehicles that spend long periods parked.
What Is E10 Petrol?
E10 is standard unleaded petrol that contains up to 10% bioethanol. The “E” stands for ethanol, and the “10” shows the maximum percentage in the blend. It is the fuel most drivers now see first at the pump, and most modern petrol cars are compatible with E10 petrol.
Why Does Petrol Contain Ethanol and What Is Bioethanol?
Bioethanol is a type of renewable fuel that is made from plants like wheat, corn, and sugar beets. It is blended into petrol to reduce the amount of fossil fuel in each litre.
Blending ethanol into petrol can help lower overall carbon impact and reduce reliance on imported oil. It is one of the ways fuel has been adjusted to balance everyday driving with wider environmental goals.
However, the benefits are not the same for every vehicle, which is why the type of fuel a car uses is still important.
Why Was E10 Introduced in 2021?
E10 replaced regular unleaded in September 2021 as part of a wider move to cut transport emissions. According to the Department for Transport, the switch could reduce carbon output by around 750,000 tonnes a year by increasing the amount of renewable ethanol in standard petrol.
It also helped create demand for bioethanol made from domestically grown crops. In simple terms, E10 was introduced to make everyday petrol a little lower in carbon while supporting domestic fuel production.
E10 vs E5 Petrol: Key Differences in Performance, Emissions & Usage
At most filling stations, E10 is the standard pump, and E5 is the premium option. The real difference is not just ethanol percentage, but how each fuel affects price, compatibility, fuel economy, storage, and everyday use.
| Feature | E10 Petrol | E5 Petrol |
| Ethanol content | Up to 10% | Up to 5% |
| Usual pump type | Standard unleaded | Super or premium unleaded |
| Typical octane | 95 RON | Usually 97–99 RON |
| Price | Usually cheaper | Usually more expensive |
| Fuel economy | Can be slightly lower in some cars | Can be slightly better in some cars |
| Best suited to | Most modern petrol cars | Some older, classic, and performance cars |
| Emissions | More renewable fuel, so lower overall carbon impact | Lower ethanol blend, but less carbon-saving potential |
| Storage stability | Less ideal for vehicles left unused for long periods | Often better for cars that sit unused |
| Chemical Stability | Lower stability: High risk of moisture absorption (hygroscopy) and phase separation over 3+ months. | Higher stability: Lower ethanol content means less water absorption and a longer shelf life in the tank. |
What is Phase Separation?
When E10 petrol sits in a tank for too long, the ethanol absorbs so much water that it sinks to the bottom. This creates a 'sludge' that can rust your fuel tank and clog your fuel pump, leading to expensive repair bills.
Which Cars Can Use E10 and Which Should Avoid It?
Most petrol cars made from 2011 onwards can use E10 without a problem. Many petrol cars built between 2000 and 2010 can use it too, but this varies by make and model, so it is worth checking before you fill up.
Cars that may be better off avoiding E10 include:
- classic cars and vehicles over 20 years old
- some early-2000s petrol models
- older motorcycles and mopeds
- some small petrol engines, such as lawnmowers and generators
If you are unsure, check the fuel flap, owner’s manual, or manufacturer guidance. A single mistaken fill is not usually a disaster, but if your vehicle is one of the models that may not suit E10, regular use is best avoided.
How Can You Check If Your Car Supports E5 or E10 Fuel?
A quick check can save you the hassle of using the wrong fuel.
- Look inside the fuel flap. Many cars have a sticker showing whether E10 is fine or if E5 is recommended.
- Check the owner’s manual, which should confirm the right petrol for your engine.
- Use GOV.UK E10 Checker
You can also use our car reg checker to look up your vehicle registration details and verify your car's exact engine specifications.
If you still cannot confirm it, E5 super unleaded is usually the safer option. It can be used in petrol cars that may not be suited to E10.
Can You Mix E5 and E10 Petrol Safely?
Yes, you can mix E5 and E10 petrol, and a one-off top-up is not usually a problem. If you accidentally put E10 in a car that normally runs on E5, just go back to E5 at the next fill-up.
The main thing is long-term use. If your car is not designed for E10, regular use is best avoided. In that case, stick with E5 as your usual fuel.
What Happens If You Use the Wrong Petrol in Your Car?
Using the wrong petrol is not always a disaster, but the outcome depends on your car and how often it happens.
If your car is designed for E10, using E10 is completely fine. If you use E5 instead, that is also fine. The car will run normally, but you may end up paying more for fuel than needed.
If you accidentally put E10 into a petrol car that is not suited to it, one fill-up is unlikely to cause immediate damage. You might notice rougher running, but no need to panic just yet. Switch back to E5 at the next fill.
The risk increases with repeated use. Over time, E10 can degrade older rubber seals and hoses. For classic car owners, this is a serious safety concern: damaged fuel lines can lead to leaks and engine bay fires. If you smell petrol while driving an older vehicle, stop immediately and check your fuel lines.
A one-off mistake is usually manageable. Regular use of the wrong fuel is where the real problems begin.
Does E10 Petrol Reduce Fuel Economy Compared to E5?
Yes, slightly. E10 contains less energy per litre than E5, so fuel economy can be a little lower. That usually means around 1% to 2% fewer miles per tank. On a 400-mile tank, the difference may only be a few miles, so most drivers barely notice it day to day.
Even so, E10 is often still the cheaper option overall because it usually costs less per litre. A small MPG gain from E5 does not always cancel out the higher pump price.
If you want the clearest answer for your own car, monitor your vehicle's mileage and fuel economy over a few full tanks rather than judging it from one journey.
Why Do Some Cars Perform Better with E5 Petrol?
Some cars work better with E5 because it has less ethanol and usually a higher octane rating. For older or classic vehicles, that lower ethanol content can be gentler on seals, hoses, and other fuel-system parts that were not designed for stronger ethanol blends.
E5 can also suit some performance cars, where the higher octane may help the engine run more smoothly. It is often a better choice for vehicles that spend long periods parked, too, because fuels with more ethanol can absorb more moisture over time.
Is E5 Petrol Worth the Higher Price in 2026?
In 2026, E5 is usually only worth the extra money if your car needs it, spends long periods parked, or genuinely runs better on it. For most modern petrol cars, E10 remains the more sensible everyday choice. With UK E10 averaging around 140p per litre in mid-March 2026 and still rising, and E5 often costing 15–20p more per litre, the extra cost of a full tank is increasingly hard to justify for standard commuters.
Is E5 Petrol Suitable for Classic and Older Cars?
Yes, in many cases, E5 is the safer choice for classic and older petrol cars. Lower ethanol content means it is usually kinder to older hoses, seals, gaskets, carburettors, and fuel tanks that were not built for stronger ethanol blends.
If you run a classic or older car, you should:
- Use E5 super unleaded where possible
- Consider a fuel stabiliser if the car sits unused
- Look for ethanol-free petrol if available
- Upgrade older fuel-system parts to ethanol-resistant materials if needed
For many older vehicles, the issue is not performance alone. It is long-term protection.
Where Can You Find E5 and E10 Petrol in the UK?
You will usually find E10 at the standard unleaded pump, often marked “E10” or “95”. E5 is normally sold as super or premium unleaded, usually labelled 97 to 99 RON.
Names such as V-Power, Ultimate, and Supreme are commonly used for E5. Pump-handle colours can vary by brand, so it is always better to read the label than rely on colour alone.
FAQs
What is E5 petrol now called?
E5 petrol is now usually sold as super unleaded or premium unleaded rather than standard unleaded. At the pump, it is often labelled 97 to 99 RON.
Does E10 go off faster than E5?
Yes, it can. E5 is often a little more stable in storage than E10 because it contains less ethanol, which means it is less likely to absorb moisture over time. That can make E5 the better option for cars that are used less often or left parked for long periods.
Can you use E5 in a car designed for E10?
Yes. If your car is designed for E10, you can also use E5. It should run without a problem, but E5 usually costs more, so most drivers only choose it if they want the higher octane or prefer it for a car that is driven less often or runs better on premium fuel.
Is E5 or E10 petrol or diesel?
Both E5 and E10 are petrol, not diesel. The labels refer to petrol blended with different amounts of ethanol: E5 contains up to 5% ethanol, while E10 contains up to 10%.
