DervMan wrote:

Brand Type Fills MPG MPH
ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph
BP Ordinary, 8 fills, 50.2 mpg, 38.9 mph
BP Premium, 6 fills, 51.0 mg, 38.1 mph
Shell Ordinary, 44 fills, 49.8 mpg, 37.9 mph (my control fuel, 'cos I use
Shell the most often)
Shell Premium, 8 fills, 49.7 mpg, 36.5 mph
Tesco Supermarket, 3 fills, 48.8 mpg, 37.3 mph
Total Ordinary, 3 fills, 47.4 mpg, 36.2 mph


The data above might suggest that Shell V-Power Diesel is slow and thirsty.
It just means that over these tanks the Saab spent longer in the city.

I would look at you Shell Ordinary fills and see if they do support the
apparent trend that your mpg is proportional to your mph. And then you
can conclude that Tesco has too much bio, and the premiums are better.