Not sure about petrol, but when I had my LPG V70 it would definitely run better and give more mpg when I filled up with "branded" gas as opposed to supermarket gas.
The technician who serviced the gas system once told me that he could tell the difference between cars run on cheaper supermarket gas because their LPG filters were always more clogged up with sediment. (He used a more descriptive term rhyming with "hit"!).
His theory was that the big oil companies refined their own product and so had better quality control, whereas the supermarkets bought any old rubbish from anywhere, just as long it was cheap.
Not sure if the same applies to petrol, but it kind of makes sense.
The other thing is, BP, Shell and the like do all market their premium products as having performance and economy benefits. And it is illegal to make claims for a product unless they're demonstrably true.
Others may post answers that argue that petrol is all made to a standard, and others will argue the opposite and produce science to prove the point.
But I'd tend to agree with the notion that the premium fuels do indeed have benefits.
Jack
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