If you drive a petrol-powered car, you'll no doubt have noticed different options when you pull up at the pumps to refuel.
As well as plain old unleaded, you can also spend more to buy super unleaded, which is usually accompanied by fancy graphics on the pump and often claims that it’s better for your car’s engine.
But are these claims true?
Exactly what is the difference between unleaded and super unleaded fuel, and is it worth spending the extra money for super? This guide explores those differences and explains the benefits and considerations for choosing the right fuel for you and your car.
What is unleaded petrol?
The term “unleaded petrol” may seem unusual for younger drivers, but it was coined at a time when petrol contained lead, because it helped engines run more smoothly. Perhaps unsurprisingly in hindsight, this wasn’t friendly to either people or the planet, and in the 1980s unleaded petrol was introduced, with leaded petrol removed from forecourts in 2000.
Today, the standard unleaded petrol is known as E10, due to its 10% ethanol composition, which helps to reduce harmful carbon dioxide emissions from a petrol engine’s exhaust. Unleaded petrol also has an octane rating, which measures the fuel’s ability to reduce “knocking” during combustion in the engine. This is when fuel burns unevenly, creating a noise and, potentially, damage.
Unleaded petrol typically has an octane rating of between 91 and 95 RON (research octane number). The higher the number, the better the fuel resists knocking. Most engines are designed to work with 95 RON fuel, although some older or low-powered cars can also function with 91 or 92 RON.
What is super unleaded petrol?
Super unleaded petrol is a premium version of standard unleaded fuel. Its standout feature is its higher octane rating – typically 97 to 99 RON. This makes it particularly suitable for high-performance engines that require more efficient combustion and fuel compression to get the maximum power output.
You’ll see super unleaded marketed by different brands using various terms, including words like Premium, Ultimate and Supreme, but the crucial factor is the higher octane rating, which makes it more resistant to knocking. As this can be particularly damaging for performance cars, many manufacturers of such vehicles actively recommend using super unleaded petrol over standard.
Another factor of super unleaded is that it’s categorised as E5 fuel, because it uses 5% ethanol rather than the 10% found in standard unleaded. It’s therefore better suited to older cars that don’t cope well with E10 fuel.
The downside of super unleaded? It’s more expensive – typically by 5p to 10p per litre over standard, which means a few extra pounds in a full tank of fuel. Is it worth the extra expense? Well, we’ll get to that in a moment.
Most producers of super unleaded petrol also include extra additives in the fuel, designed to improve engine performance and longevity. These vary from brand to brand, but they typically include detergents to prevent and remove carbon deposits from the engine, anti-corrosion agents to protect the engine from rust and degradation, and friction modifiers to reduce wear and tear on moving parts. Sometimes octane enhancers are added to further boost the fuel’s octane rating.
These additives won’t impact an engine’s immediate performance, but they can help reduce engine wear and prolong its life in the long-term. They can also help clean engines that have deposit build-ups after running on regular fuel, which can improve efficiency.
Can you switch between standard unleaded and super unleaded petrol?
Yes you can. Most cars from the last 20 years will be happy with either standard unleaded or super unleaded fuel, and it’s not a problem to mix them.
What benefits could I see from switching to super unleaded?
You’ll see the most benefits from super unleaded fuel if you have a car with a high-performance engine – think hot hatchback level and upwards. These engines are designed to maximise power output and super unleaded fuel will help them operate more efficiently. You’ll likely see a small increase in fuel efficiency as well as extra power.
That said, such cars can run on regular unleaded without any serious consequences, because the car’s computer systems will adjust the engine’s running to compensate for the lower octane rating in the fuel.
You should theoretically see efficiency and performance improvements in regular, non-high-performance cars too, but they’re likely to be smaller, to the point where you probably won’t notice them.
Is super unleaded petrol worth the extra money?
The answer to this question is “it depends”. Factors to consider include what car you have and how you drive it.
To do some quick maths, assuming super unleaded costs 10p a litre more than standard, on a 55-litre fuel tank that equals an extra £5.50 per visit to the pumps. If you fill up every two weeks, that’s around £140 added to your annual fuel bill.
If you have a high-performance car, that extra money is probably worth it. High compression engines are designed to run on higher-octane fuel, and using super unleaded will unlock their power potential and improve their fuel efficiency.
Super unleaded is also probably worth it if you do a lot of long drives, as the small benefits in fuel economy will add up.
However, if you drive a regular small or medium-sized car, you’ll find the difference in performance is negligible, and regular unleaded fuel is probably sufficient. If you want the benefits of the various additives that producers add to super unleaded at the pump, you can buy them separately and add them to your fuel tank yourself to help keep your engine clean.
Which type of petrol is greener?
When it comes to environmental impact, standard unleaded fuel has the advantage due to its E10 rating. The extra ethanol content helps reduce carbon emissions by replacing fossil fuel with bioethanol, which comes from renewable sources.
That said, because of the additives found in super unleaded fuel, cars running it could see their efficiency improved, which itself can reduce emissions.
So which type of fuel should I use?
To decide whether unleaded or super unleaded petrol is right for your car, first consult the handbook. This will usually give you a recommended octane rating based on its design, which should maximise its performance and longevity. From 2021 onwards the UK’s standard unleaded is E10, but some older vehicles can only use E5, which means you’ll need super unleaded. If your car is older than around 20 years, check to see if it’s compatible with E10.
In the long run, both petrol types will face increasing competition from electric vehicles (EVs), as the UK approaches the 2035 ban on the sale of new non-electrified petrol and diesel cars.
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