It’s a hotly debated topic, and the last time PetrolPrices did some simple desktop research around the issue, around 40% of drivers thought that supermarket fuel was an inferior product compared to branded fuels, some drivers even mentioning that they can feel a difference as soon as they fill up.

But is that really the case? Or is there an element of the placebo effect?

For clarity, we’re talking about the absolute standard fuel, no special blends or high octane ratings, no ‘super’ or ‘premium’ tags and no claims to special additives to cleanse, improve, repair or cure anything; standard unleaded or diesel fuel – generally the cheapest at the pump.

Engine efficiency

It’s long been known that car manufacturers were prone to being a little optimistic when it came to claims of fuel efficiency, power or emissions produced, but the reality is that a minor shift in environmental conditions could significantly change how an engine worked.

Air pressure, density, temperature and humidity can all play a part, and to counter those variables, a modern fuel-injection system uses a vast array of sensors to measure, check and adjust the engine accordingly; gone are the days of having to ‘re-jet’ the carb for particularly fine-tuning – the FI system does it all.

This, in theory, means that you could drive your typical car from here to the heights of Mt. Everest and then onwards to Timbuktu without having to change a thing, both in terms of environmental changes and petrol quality – the system will optimise the fuelling using short and long-term adaptive mapping.

Consistent fuel quality

All fuel sold within the UK is governed by national and international standards, and all petrol stations use the same base fuel, whether that’s at the largest supermarket petrol retailer (Tesco) or independent fuel retailer using ‘branded’ fuels – the base fuel comes from the same refineries.

Whilst it’s true that additives are used in all the fuel blends, including the ‘standard’ unleaded or diesel, these additives are an industry secret, but you can be sure that they’re all similarly … low-grade, or they’d come under the super fuel bracket, and advertised as such (with an increase in price to reflect the additives).

There is an argument for fuel going ‘stale’, in that it loses some of its volatility over time, but this really only happens when exposed to the atmosphere; the hygroscopic nature of fuel drawing in moisture from the air – a totally sealed container of fuel should last almost indefinitely. But this means that fuel tanks that are replenished more frequently should (in theory) be less likely to cause a problem.

Perceived value

Perhaps part of the problem is psychology; supermarkets are experts at taking branded products and making them their own – a premium breakfast cereal, for example, is no longer “Crunchy Super Nuggets” but “Nuggets of Super Crunch” – could it be that drivers feel supermarkets are doing the same with fuel?

The fact that they’re generally cheaper than the competition would help that thought process along; they’re paying less than the branded version, therefore the product is similar, but doesn’t quite live up to the same standard?

We’ve also heard reports of some supermarket chains occasionally buying their fuel from elsewhere in Europe, bringing it across by the tanker load. And whilst that could alleviate a supply issue, it’s doubtful that it could ever be financially viable to make it a long-term solution, and yet the fuel would still be covered under European regulations.

Actual difference

There is no doubting that some fuel consumers have had problems after filling up at a supermarket, but these problems are one-offs, not an everyday occurrence. Despite holding fewer petrol retailing sites, the supermarkets actually account for 45% of all fuel sales; when the figures are corrected for sites-vs-litres sold, they actually have the majority of sales.

Due to the nature of modern fuel-injection systems, it’s entirely possible that a vehicle could alter the fuelling strategy per tank of fuel, but under normal circumstances (assuming the fuel quality was typical), this would only be noticeable under extreme loads, not through typical driving.

The only way to give an absolute definitive answer would be through expensive and extensive testing, using a controlled-environment in a dynamometer test-cell, where all influencing factors could be controlled and repeated 100%. Owners claims that a vehicle loses performance, increases mpg or runs differently can really only be treated as hearsay – industry insiders will tell you that a ‘seat of the pants dyno’ will only really notice a 10% difference – nowhere near accurate enough to gauge the quality of fuel.

Do you think supermarket fuel is inferior to branded? Have you noticed a change in performance when filling up with either? Or are you just paying an added premium? Let us know in the comments.

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