A quick and much easier way to find out the average miles per tank, and could be easily implemented would be to take the avg mpg for that car, find a % that you like of the rated gallons for the tank (that you could use for all of the cars) and multiply that amout with the mpg avg. That would give you the average miles per tank An example: HCH I CVT ULEV 45.2 (current avg mpg) x 13.0 (98.5% of tank capacity) = 587.6 miles per tank. HCH I CVT AT-PZEV 45.2 x 11.7 = 529.7 HCH I MT ULEV 48.0 x 13 = 624 HCH I MT AT-PZEV 48.0 x 11.7 = 562.5 HCH II CVT 45.6 x 12.1 = 552.4 Prius II 47.8 x 11.7 = 560.2. Continue this for all of them.

Summary:

HCH I CVT ULEV = 587.6
HCH I CVT AT-PZEV = 529.7
HCH I MT ULEV = 624.0
HCH I MT AT-PZEV = 562.5
Prius II = 560.2

Simple math that could be added to the top of the compare section. I know nothing of web design, but I don't think it would be hard to add and would give you an idea of what is attainable. It would be nice to have a top ten list of the most miles on a single tank, and a 1000+ mile tank club. special stars or colors ... just an idea.