I tried searching around to see if anybody else has requested this, but didn't find anything exactly like it.
I got to thinking that it would be valuable to be able to see MPG for a given fuel rating (octane, cetane, whatever) and brand. Perhaps one brand is consistently better than another, or perhaps, for a given model, octane affects efficiency. People argue whether it does or not - but we have the power and data to actually show statistically whether it is true.
I recall recording mpg (on paper) back in the day on my '94 Grand Am, and tried to see if the octane affected my mileage. At the time, I concluded that using higher octane did indeed boost my mileage, and effectively paid for itself. Granted, the price difference then between each grade was only about $0.10/gal difference :-)
At a minimum, I'd like to have the brand/fuel rating data available when I export my fuel-ups in a CSV format. Right now, fuel type/rating isn't exported. I believe brand is.
A stretch goal would be to show aggregate information for all users. Does Shell get on average +1MPG than, say, BP? For a given model/year/engine vehicle, which octane rating achieves peak mpg? A graph or simply an average would be nice.
We all have choices in where we buy fuel, and then when at the pump, which grade to select. It could help people save money, and burn less fuel, help the environment, etc if we can see that data in a useful way.