A question of petrol?

[iBozz]

Back in the early 1970s there was a real threat of petrol rationing and, consequently, lots of advice about how to conserve fuel and get the best mpg out of the allowance.

Fortunately rationing never came in, although a blanket speed limit of 50mph did which is why many of us who were around then will say, when asked, that that is the current speed limit on single carriageway roads!

But I digress.

One piece of advice was to mix brands of petrol at each fill up and not to stick to one single brand.

For some time, in a 2012 Nissan Micra, I have been getting around 55mph on the journey between Manchester and London on Motorways using solely Shell Fuelsave as that happens to be what my local garage sells.

Having to travel around more recently, I have been filling up wherever petrol is cheapest and the tank now contains, in varying proportions of course, a mixture of Tesco, Asda, Morrisons and Shell and on a return trip between Manchester and Penrith, again on Motorways, I averaged 61mph driving in my "normal" style.

Does this prove that the old advice to mix brands was correct or is this merely the result of other external factors such as weather, hills encountered, etc.?

Are some fuels better than others (if so which) for mpg or is it all hogwash and they are all, to all intents and purposes, the same?

Thanks in advance.