Do you not remember that news event a few years ago when everyone filling up with supermarket fuel kept breaking down? I still struggle to forget that when I think of filling up. That's why I'd consider proper fuel companies' 97 in the same bracket as Tesco 99
That was an isolated incident back in 2007 linked only to the Vopak refinery in Essex though, only really affected the SE and was due to silicon contamination of the storage tanks and whilst it was a major cock-up its unfair to tarnish all supermarket fuel inferior without knowing the facts imo..
I've been in many Tesco stores and still haven't noticed where they are hiding the onsite petrol refinery (even looked behind the bakery once) so lets consider where they and the other retailers actually get the fuel from
Tesco for example part own 'Greenenergy' and thus use them for distribution of fuel throughout their network but as there are only 7 Greenergy managed terminals in the UK they also use 3rd party terminals for the supply of fuel depending on location, for example my local terminal is 'Stanlow' in cheshire which happens to be the sole producer of Vpower for the entire UK and if you were to spend some time truck spotting outside the main gate you'll notice Tesco, BP, Texaco tankers happily going in and out...
Therefore depending where you live in the UK and if buying Tesco 99 you will either get exactly the same base fuel from the same tanks as Shell / BP etc but with Tesco's additive package added at source, in other locations it will come straight from Greenenergy to Tesco specification
http://www.greenergy.com/Our_business/fuel_terminals.htmlIt's fair to add that Vpower's formulation is not shared by shell and is transported from Stanlow via the pipeline network to Essex to aid distribution so you could argue that will guarantee some consistency of quality but i'd still argue that Tesco 99 is right up there in comparison
More important imo is ensuring you fill up from 'busy' filling stations as high octane fuels 'go off' quicker than regular blends so try and use stations that have frequent deliveries to avoid old fuel