Don't be conned by all the hype from the oil companies!
Fuel is a centrally marketed commodity and they all buy refined products from each other so when you pull into a Shell station you could well be filling up with fuel from Total, ExxonMobil, ChevTexaco etc etc.
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Absolutely Mr Morse all the petrol in Scotland comes from the same refinery in Grangemouth.
Was told that the only difference was that the Shell tanker drivers arrived with a can of "stuff" that they put in before they filled up and swerved around a bit on the way out to mix it up, viola Optimax :D