| I think that petrol vaies from supplier to supplier. Are you judging a level field here with fuel from the same garage?
I hired a petrol van once and the yard was behind a Fina garage. It had no fuel in it so I had to fill up there. It ran rough as hell all the way down to london and used a tank of fuel to do it (just over 100 miles). I filled up at services there and it ran like the proverbial **** off a shovel all the way to Bournemouth and got far better mileage. Needless to say, never used Fina again! Cound have been dodgy fuel from any of them though really. | 
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