Premium fuel is a feature of most service station forecourts. Compared to regular petrol or diesel it will usually have a racy sounding name such as V-Power Nitro+, Momentum or Synergy Supreme+. And there will be various claims that these fuels ‘defend against gunk and corrosion’ or ‘maximise performance’. And of course there’s a suitably inflated price tag to go with them. But for many drivers, the question remains: are they worth the extra money?
How much extra does premium fuel cost?
According to Petrolprices.com, the average price of regular unleaded petrol is 115.5 pence per litre (PPL). The average price for premium is 126.3PPL. If you fill up with 45 litres, regular petrol will work out £4.86 cheaper every fill. With diesel, regular costs on average 117.4PPL and premium 130.86PPL, a difference of £6.04 per 45-litre fill
Do the sums work?
Assuming the car does 40mpg on the regular fuel, for the premium diesel to pay for itself, it would have to improve fuel consumption to 44.6mpg. Anyone who’s played around at increasing their car’s economy by changing their driving style will know this is a significant margin. According to Esso, its Synergy diesels boost mpg by 1.8%. That would increase a 40mpg car to just 40.72mpg. Esso doesn’t make any claims about its Synergy Supreme+ diesel.
Will premium fuels improve economy?
You could spend a lifetime searching internet forums for the answer to this and never come to a reliable conclusion. And it’s further influenced by the car you run, how you drive it and the type of driving you do. However, independent tests by What Car? revealed there was little if any improvement in economy when its testers compared regular and premium fuels on the same cars.
What is premium petrol?
Firstly, and rather confusingly, many petrol pumps will call regular fuel ‘premium’ and premium fuel ‘super’. We’ll call regular ‘regular’, and premium ‘premium’. To understand whether premium fuel is worth the extra money, it’s worth understanding how it works.
With a petrol engine, it’s all down to the octane rating. This is a measurement indicating how much energy it takes to ignite the fuel. Premium petrol usually has a higher octane rating than regular. Premium petrol also has more in the way of cleaning agents and additives. The claim is that by keeping the inside of an engine clean there’s a reduction in friction and consequently the motor runs more smoothly and efficiently.
Do some cars need premium fuel?
Some petrol engines – usually in performance cars – have what’s known as a high compression ratio. The engine compresses the fuel and air mixture inside the cylinder more than regular engines. Then when the mix ignites, there’s a bigger bang. Engines that have higher compression ratios need fuel with a higher octane rating or the fuel will combust too early in the cylinder, causing a condition called knocking or pinking.
How do you know if your car needs premium petrol?
Inside the fuel filler flap, it should detail what octane fuel your car needs. 95 RON (Research Octane Number) describes regular petrol. It will say 97 or 98 RON if your car needs premium petrol. If there is no sticker, check the owner’s manual or call the dealer for your make of car. If your car says use regular 95 RON unleaded, use that. All fuels sold in the UK have to meet European standards. And those sold by big name brands will have sufficient detergents and additives to keep the engine running beautifully.
What about premium diesel?
Rather than octane, diesel has a cetane rating. As diesel works simply on compression with no spark, the most efficient way is for it to ignite as quickly as possible. Fuel that does this has a higher cetane rating. While regular diesel has a cetane rating of around 48-50, premium diesel might have one that is 55. In addition, premium diesel will usually have more additives in it to keep the engine cleaner.
If you have a car that suggests you run premium fuel, do so. If yours doesn’t you won’t be doing it any harm by sticking with regular fuel. Our advice would be to note how many miles you get out of a tank full of your regular fuel, then try a tank full of premium and see if the sums add up. However, you might well find that simply having your car regularly serviced will reduce fuel consumption as much as paying extra for fancy fuel.
James is a motoring journalist and former magazine editor at BBC Top Gear and Auto Express. He has scooped, reported on and reviewed most new cars of the past 20 years, and currently contributes to the Driving section of The Sunday Times.