Whether you use supermarket fuel, branded unleaded petrol, diesel, or one of the “super” fuels, the chances are you’ve sometimes wondered about the quality of the liquid you’re feeding into your vehicle.

Our recent survey, conducted towards the end of last year, certainly raised many queries from members regarding fuel quality, especially in reference to the differences between supermarket and “name brand” petrol and diesel. Many of you were also very curious about the real-life benefits of paying extra for “Super” fuels instead of sticking to the cheaper standard options.

In response to the hundreds of queries we received, we decided to help out and find you some answers, based on in-depth research and expert opinion. While we suspect that some of our findings may prove controversial, we hope we’ve managed to distil the current “conventional wisdom” on these issues – so read on to find out more.

How we approached our study?

When we sat down to discuss this study, one of the PetrolPrices.com team pointed out that he had a friendly scientist in his extended family – a specialist in biochemistry. Speaking to him seemed a good place to start.

He told us that fuel science is essentially centuries old and very well researched, and was able to point us to some good sources of information. He also provided us with his own view on the controversial topic of supermarket fuel – so let’s start there.

Supermarket Fuel vs. Branded Fuel

Our friendly scientist was very clear on his view regarding supermarket fuel. He said the following:

In the UK, all pump gasolines and diesels are governed by various national and international standards – notably European and CEN Standards. These require vehicle fuels to conform to minimum world-agreed quality and performance standards… so in Europe,  supermarket fuel is as good as any.

We can already hear the sharp intake of breath from some readers, because this is a fiercely debated topic. Just look at any article or forum thread on the subject and you’ll hear people passionately arguing that supermarket fuel is inferior.

We were curious about just how common this view was amongst UK drivers, so before completing this article we carried out a quick Facebook survey asking whether people think supermarket petrol is inferior. The results of our survey suggest that around 40% of drivers really do suspect that there is something “less good” about supermarket fuel.

However, our friendly scientist is far from alone in his opposite opinion. A recent study in The Telegraph on the same subject cited spokesmen from both The RAC and The AA saying much the same, with the AA representative stating that “petrol and diesel fuel quality is governed by the same European standard, whether it is sold at a supermarket in Manchester (or) an independent outside Mevagissey.”

This seems pretty conclusive, and is backed up yet further by plenty of anecdotal reports online from consumers who have witnessed supermarket and name-brand tankers both stocking up at the same places.

However, there is a little more to this. As explained in a report in The Express, all petrol and diesel is made up of a base fuel and an additive mix. The additives the supermarkets and the various other brands choose to use will not necessarily be the same. The differences shouldn’t be significant enough to effect fuel economy or the “quality” of the driving experience, but this factor could have some part to play in the fact that some individuals are utterly convinced that supermarket fuels are in some way “different.”

This aside, we have to conclude that there is absolutely no scientific basis on which to assume that supermarket fuel is “bad” or unsafe. Around half the fuel powering the cars on Britain’s roads, right now, came from supermarket pumps – so if there was something wrong with it, we’d know by now. Even so, we’re ready for the inevitable debate!

Super Fuels vs. Premium / Standard Fuels

The other big question our members asked when we conducted the survey was what the real difference is between standard fuels and the “super” versions we see on forecourts for more money. At the time of writing, these come in at around 10 to 12 pence per litre more – so choosing to use them instead of their standard equivalents is a fairly pricey decision.

The first matter to clear up is any confusion between “premium” and “super” fuels. Standard 95-octane unleaded petrol is sometimes called “premium unleaded,” so we mustn’t confuse this with the more expensive “super” fuels, which are 97, 98 or even 99-octane.

Some examples: BP offer “Ultimate” unleaded, Esso call theirs “Synergy Supreme Plus,” and even Tesco have a “super” petrol of their own called “Momentum 99.”

So, do these fuels make any difference to how your car runs?

It seems that in many cases, the answer to this question is indeed “yes.”

We had a look in the instruction manual for one of the PetrolPrices.com team’s car – a 2.0FSi Seat Leon. The manual actually specifically recommended using “Super” unleaded, at 98-octane. It turns out that many car manufacturers make the same recommendation, especially when it comes to performance cars.

Let’s look at the science: The octane rating of petrol (or the cetane rating, in the case of diesel) describes how efficiently a fuel burns when used in a combustion engine. The higher the octane figure, the higher the efficiency. As per this report, a higher number can mean better performance and / or better fuel economy – though whether you’ll notice it on your daily commute will depend much on your driving style, your vehicle, and your attention to small details!

The octane or cetane ratings are not the end of the story. “Super” fuels also usually come with a more “luxurious” additive mix to deliver better performance or economy. For example, Esso’s Synergy Supreme Plus contains “double the detergent additive” compared to Esso’s standard fuel. Shell’s V-Power Nitro+ Unleaded apparently forms “a protective film on metal (to help) prevent corrosion.”

Once we get down to these additives, it’s all a little like comparing shampoos and toothpastes. There are probably some motoring enthusiasts who swear by a particular brand for a particular reason. However, the octane or cetane rating of a fuel is a more scientifically relevant way of comparing “standard” to “super.”

So should you use “super” fuel in your vehicle? Well, we’d suggest looking in the manual for your car to begin with, just like we did. If your manufacturer points you in the direction of high-octane fuel, you may want to stick with their advice.

However, unless you have a performance car or a “hot hatch,” you’re probably fine to stick to the standard stuff. This is a view supported by Matthew Minter, the Editorial Director for Hayne’s Maintenance Manuals, who says that “99% of cars will work perfectly well on 95-octane standard unleaded fuel.”

If you choose to defy the advice of your manufacturer, it has to be your own decision. For what it’s worth, that Seat Leon we mentioned above has worked just fine with standard 95 petrol, but our inclination is to go with the manufacturer’s advice – particularly as there is science to back up the use of higher octane fuel.

What About Fuel Additives?

Another option open to you is to use a third-party fuel additive such as Redex. These often claim to improve both performance and miles per gallon, and are an inexpensive “treat” for your car.

Essentially, these products perform the same kind of function as the additives in “Super” fuels – primarily keeping engines clean and lubricated.

However, as far back as 2009, Auto Express reported on a Which? study that described such additives as “a waste of money.”

There are sure to be some drivers and mechanics who use and trust these products, but the science doesn’t seem to agree. One thing Auto Express seemed very clear on is that they certainly don’t offer any kind of octane boost to rival that of a “Super” fuel.

Supermarket Fuel and “Super Fuel”  – Our Conclusions 

Our research into these fuel quality questions has produced some fairly clear answers. However, we suspect, based on the voracity of some of the motoring enthusiasts who frequent the forums, that plenty of people will still debate our findings.

In brief, our research throws up the following conclusions:

  1. There’s no scientific evidence to suggest that supermarket fuel is inferior to its brand-name equivalent.
  1. There are some proven benefits to using more expensive “super” fuels, but these benefits are only really pronounced in sporty vehicles.
  1. Third-party fuel additives don’t seem to stand up to their bold claims when tested. However, some people state additives work well for them. You could try them for yourself to see if they make a difference, as they cost just £5 a bottle so may be worth trying – if only once!
Would love your thoughts, please comment.x