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