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Most fuel brands offer “premium” or “super” unleaded petrol that they claim improves your car’s performance and helps to protect your engine, while cutting your fuel consumption.
However, with these souped-up fuels costing up to 10p more per litre than standard unleaded petrol, the question is whether they are worth the extra outlay?
We wanted to know. So here are the results of our investigation into exactly what benefits super unleaded is supposed to offer, and whether it delivers on those promises.
What is premium fuel?
Premium fuel is more expensive than standard due to its higher research octane number (RON) - the benefits of this increased octane rating include lower fuel consumption as well as better engine protection and performance.
BP said of its premium fuels: “Our hard-working, BP Ultimate fuels help your engine to run at its most efficient, so as little precious energy as possible is wasted – helping you get more miles from your tank.” In the UK, standard unleaded now has a RON of 95, while super unleaded is around 98 RON.
Some petrol companies also market a top-of-the-range fuel with a RON of 102.
What's the price difference between standard and premium fuels?
According to the petrolprices.com, the average price of a litre of unleaded petrol is currently 103.49p per litre, with super unleaded costing over 11p more at 114.05p per litre.
Diesel drivers can expect to pay £104.01 per litre of standard fuel, and £116.94 per litre of premium. And petrol users should be aware that standard unleaded is often marketed as “premium”, which could lead to some confusion.
As a rule of thumb, it's generally 'super' for petrol and 'premium' for diesel.
Does super unleaded improve mileage?
The higher octane rating of super or premium unleaded petrol should make it burn more efficiently, thus delivering more power for less fuel burned.
But while some drivers report noticing a small increase in the numbers of miles they could do before refilling the tank when using super unleaded petrol, others find that there is very little difference. It seems to depend on a range of factors such as how you drive and what type of car you have.
The best way to discover if premium unleaded petrol can help to reduce your fuel consumption is therefore to fill up with it, say, three times and see if you notice any difference.
If not, you’re probably better off sticking with regular petrol – especially if saving money is your main aim.
Does super unleaded improve performance?
As with consumption, the increase in performance you can expect with super unleaded petrol will depend on the car you have, the way you drive it and what sort of journeys you go on.
Higher-octane fuels suit high-performance engines where pressures and temperatures are greater and it can therefore be used to up the amount of available horsepower and improve performance – if your car’s engine is built with performance in mind.
Regular engines, on the other hand, do not come with the same compression ratios and engine temperatures as turbocharged and supercharged engines, meaning they get a lot less out of the high-octane characteristics of these fuels.
Generally speaking, owners of higher-performance cars will get the most out of premium petrol as a result – especially if they are often driven hard on open roads.
But drivers of vehicles with smaller engines that are used for little more than local errands and the weekly shop are unlikely to see any significant benefit.
Does super unleaded reduce engine wear and tear?
Higher-octane fuels help to prevent so-called ‘engine knock’, which is when unburned fuel pre-ignites in a vehicle’s engine, often damaging interior components.
The higher the RON of a fuel, the more likely it will be to burn in a controlled manner in the engine, thus lowering the chance of ‘knocking’.
Again, however, only motorists with high-performance cars – where engine knock is more prevalent due to the higher compression ratios caused by superchargers or turbochargers – will really see the benefit.
BP said: “BP Ultimate Unleaded is formulated to protect against wear in key engine components and guard against the harmful effects of corrosion.
Plus it contains a special formula designed to lower the friction in your engine.” Premium or super unleaded petrol also has additives that help to keep your engine clean, which should mean that it keeps working for longer.
Esso said: “Our premium grade, higher octane petrol has double the detergent additives to help give a deeper clean for better engine performance.”
Is it worth going the extra mile for cheaper fuel?
Whether you're buying premium or regular fuel, the cost-per-litre can vary significantly from forecourt to forecourt, but driving that little bit further for cheaper fuel could mean you're actually spending more money to get there than you save at the pump.
Our handy Fuel Cost Calculator will help you work out if your search for cheaper fuel is actually costing you more…