Originally Posted by milesr3
My interpretation is that Shell's claims are less bold, being focussed more on engine cleanliness as a means of maintaining optimum performance (which is hard to dispute), whereas BP go further with their claims of extra power, economy and reduced emissions and particulates based on independent testing by MIRA. In practice both fuels exhibit the same benefits, but BP should be applauded for publishing their results.
There is quite a bit of technical data out there, but I do believe they have to be a bit careful, as they are not putting each car through the official regime and getting the kind of results which cannot be challenged. We know the difficulty with mpg claims anyway. How can you be too specific when user conditions and driving is unique?
Personally I find that steady speed driving is one of the best ways to get mpg gains, as the engine is typically running at better efficiences. Smoke levels (non DPF cars) is another way to see that the combustion is cleaner and more efficient.