Premium diesel and petrol – do they work?

Is the extra cost worth the money, or is it a rip-off?

“Do premium diesel and premium petrol fuels work, or are they just a waste of money?” We get this question quite often, and there’s not really a clear-cut answer.

Most fuel brands offer ‘premium’ options for both petrol and diesel fuels, which are usually priced about 10% higher than their ‘regular’ fuels. They usually claim to give you more performance (or other improvements) while using less fuel.

So how much gain do you get, and are they worth the price premiums over regular petrol or diesel fuels?

What is premium unleaded petrol?

Premium unleaded petrol is usually a more refined form of petroleum than regular unleaded, with a higher octane number. Regular unleaded in the UK has an octane number (RON) of 91, while premium unleaded petrols from most fuel companies usually have an octane number of 95-97.

The higher octane number makes the petrol burn more efficiently, thus delivering more power for less fuel burned. It may also have additives such as detergents to keep the inside of the engine clean.

The level of improvement you can expect to get from premium unleaded petrol will depend on your engine’s requirements, and your driving style and circumstances.

Some engines, usually in higher-performance cars, require premium unleaded at all times and will suffer reduced performance and fuel economy if you use regular unleaded. These engines usually have finer tolerances and don’t respond well to lower-octane fuels.

Most mainstream petrol-engine passenger cars are perfectly content running on regular 91-octane unleaded petrol, so it is then a question of whether the extra money for premium unleaded is going to provide you with noticeably better performance and/or fuel economy.

 

Depending on your driving circumstances, many engines will see very little difference at all; if your driving is predominantly city commuting and school runs, you probably won’t notice any significant improvements. If you tend to drive harder or do more open road driving, you may notice more substantial differences.

petrol pump in a bowser at a petrol station

What is premium diesel?

Similarly, premium diesel fuel is usually a higher quality of fuel which burns more efficiently. It may also have additives which help keep the engine clean and improve cold-temperature performance.

There is usually less difference in either performance or economy between premium diesel and regular diesel than you get with premium unleaded petrol and regular unleaded for a single tankful.

However, premium diesel will potentially help your engine run smoother and cleaner, which can improve both performance and economy with regular use. This may be more noticeable on older or higher-mileage engines than in a brand new car which hasn’t yet accumulated any sediments within the engine.

Some owners have reported that premium diesel has helped them reduce the frequency of diesel particulate filter warnings and problems, but we’re not aware of any scientific studies that can back this up.

Try it and see

The best way to discover if premium diesel or premium unleaded petrol work for you and your car is to try about three tanks’ worth and see if you notice a significant and repeated difference.

If you can’t feel any improvement in performance and you don’t appear to be getting greater mileage from each tank, you’re probably better off sticking with regular petrol or diesel.

If you do notice improvements, you need to decide whether the increased cost (which can be up to 10p/litre) is justified.

Premium fuel or a bottle of additives?

Alternatively, you can add a bottle of specialised fuel additives to your tank. There are various kinds depending on whether you’re looking for better performance, better economy or both.

I ran a three-month trial of Redex fuel system cleaner earlier this year, but there are many different brands to choose from. The cost of a bottle of fuel additive is roughly similar to using premium fuel instead of regular, so give it a go and see how it affects you and your car.

fuel economy - premium petrol or premium diesel - the car expert

This article was originally published in August 2012, and was updated and expanded in December 2018.

Stuart Masson
Stuart Massonhttps://www.thecarexpert.co.uk/
Stuart is the Editorial Director of our suite of sites: The Car Expert, The Van Expert and The Truck Expert. Originally from Australia, Stuart has had a passion for cars and the automotive industry for over thirty years. He spent a decade in automotive retail, and now works tirelessly to help car buyers by providing independent and impartial advice.

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24 COMMENTS

  1. The only difference between octanes is that low octane ignites too soon in high performance engines.. Porche Ferrari etc. High octane mean it won’t ignite prematurely under pressure..!!!!

  2. My car is a 2014 Suzuki Alto with a massive 68 bhp. The cars drives surprisingly well but it obviously hasn’t got a lot of power. On the advice of a fellow owner I am using 97 octane petrol as he said it makes a difference. I can honestly say it does. Outright performance, through the gears, is very much the same as with standard petrol, irrespective of whether it is branded or supermarket. The noticeable difference is low speed torque.

    Like most motorists I use many of the same roads on a daily basis and what I have found is I can change up to a higher gear at much lower speeds than with “ordinary” fuel. Roads where I normally had to drop to a lower gear, I now find I don’t have to. I can also change up much earlier than with 95 octane, it really is that noticeable. I’m not noticing any change in fuel consumption, even though I am using fewer revs, but by not having to change gear as much as I did previously the car is far more relaxing to drive.

  3. Like most, I thought premium diesel fuel was just another con to get us to pay even more for the high price of fuel we pay now. However, I’d rum my 2010 Mondeo on supermarket fuel for about two years when I noticed it start to take a little longer to start. Once going it appeared fine. But progressively it got to the point that it wouldn’t start, and the engine management light came on.
    My local garage said the DPF was clogging up and not burning off properly. They cleared the warning light and several high revving days later everything was back to normal. After a few conversations with other diesel owners I decided to try Shell V-Power (other names are available!!). Again, after a few days there was a noticeable improvement in throttle response and a while later an improvement in MPG. The cost? I’ve calculated that it’s the equivalent of buying a cleaning additive each time a fill the tank. Only my view and I’m no scientist

    • Hi Charles. Interesting findings. I’ve just been running a long-term trial of Redex cleaning additives (other names are available!) in my petrol car. It may be worth trying a diesel cleaning product every few months and reverting to normal diesel to see if that allows you to keep the performance and economy benefits of a clean and de-clogged engine without having to fork out for premium fuel every time you fill up.

  4. Thanks for the reply Stuart, much appreciated.

    I am from Denmark and my Ghibli was bought in Denmark when it had gone 7.500 miles, so I guess its still considered as new.
    I have driven another 5000 miles so all in all it has gone around 12.500 miles.
    My only concern is the DPF if it works as it should. I use my Ghibli Diesel as my weekend fun car which I drive approximately 20-25 minutes trips or longer to dinner/events/shopping with my wife and then I have a Citroen C3 for every-day driving.

    But to understand it correctly the Premium diesel does not help the Diesel Particle filter in any way ?
    And since my Ghibli is my weekend-car I should do longer drives of minimum 25 minutes on each drive to keep the DPF working properly even if this car is from end-2014?

    Brgds,

    Jisan

    • Dear Jisan,

      I have a 210.000 km Euro 4 Alfa 159.

      Feel free to use all sort of diesel, as the newest is injection system, more precise and clean is the burning cycle. What you have to be absolutely perfect is oil and filters check and replacing. A friend of mine is a motorist, involved in motorsports, and he has a 500.000 opel astra that is taking to 1M km. He suggested to avoid special fuels as they clean very well, and for this reason the risk is to clean lubrication too. His opinion is to invest in oil and fuel frequent changes, every 20.000 kms at least. Feel free to ask me more information. Enjoy your Maserati, it’s a pleasure to know there are people passionate in so refined mechanicsm

  5. I have the Maserati Ghibli Diesel, should I only use Premium Diesel as this is a high-performance car and will this help the engine to warm up quicker and thereby let my DPF work better?

    • Hi Jisan. If your car is new, it should not give you any great benefits in terms of improving performance or economy. Premium diesel is designed for cleaning out diesel fuel systems, but it is unlikely your car’s fuel system will be clogged up unless you have put a high number of miles on your Ghibli.

  6. where can i get premium diesel in NW London will I get better performance from my 2016 Kia Ceed Crdi 7 speed dct

    • Most service stations will offer both regular and premium diesel options. As for whether it will give better performance, it’s unlikely to be noticeable. Your car is new, so it’s unlikely to have accumulated any significant sediments in the fuel system which would be affecting the engine performance.

  7. Hello ive recently purchased a Yamaha MT-125 ABS it it recommends using prem unleaded with a octane number of 95 or higher im just wondering if it will cause problems mixing reg and prem unleaded fuels. this is probable a silly question but the bike is the first vehicle ive ever brought or owned.

    • Hi Tony. If you are in the UK, regular unleaded is 95 octane anyway, so you shouldn’t have any problems. Whether or not you get better performance and/or economy running premium unleaded (97-98 octane) will depend on your bike’s engine, but it certainly shouldn’t cause any problems running a mix of the two.

    • Hi Anne. You probably won’t notice much difference in performance, unless you really drive your car hard, but you might find the economy is better. With the fall in petrol prices lately, it’s probably a good time to give it a go, since premium is cheaper now than regular was a few months ago.

  8. I have been trying this experiment in my diesel Astra for the last couple of months, and I can’t really tell the difference. So I’m going to stick to normal diesel.

  9. Hi! I have been trying this for the last fortnight, and seem to be getting better mileage from premium petrol. I worked out that it’s costing me about the same, but I guess it’s probably worth it in terms of being better for my engine, isn’t it?

  10. V-Power Diesel is a blend of regular petroleum-based diesel and synthetic diesel , created using gas to liquids (GTL), along with some extra additives designed to clean the injection system and improve injection pump and injector lubricity.

  11. I think it’s all a con, and that it’s probably exactly the same fuel in the regular and premium pumps. Just an excuse for blood-sucking oil companies to screw us all over yet again.

  12. Hi Stuart,
    What happens if both premium and plain unleaded petrol is put into the tank? Say half premium and half plain? Will the engine explode? I am asking because I have a loose memory and will surely forget what I have put into the tank last time!

    Thanks,
    Adnan

    • Hi Adnan. For your car, it will make no difference at all. Your Toyota will run happily on regular unleaded petrol, although you may get slightly more power and/or better economy on premium unleaded. So you definitely don’t need to worry about it. If a certain engine is designed to run on premium unleaded, it will not run cleanly on regular unleaded and over time may misfire and develop problems. However, it is not going to cause the engine to explode or anything dramatic like that.

      Best wishes, stuart.

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