fueleconomy.gov is a good starting point, however keep in mind when the EPA tests were done on our engines, they were done on non-ethanol fuel. Meaning that E10 you stuff down your tank kills about 2-3mpg. I remember back in 2009-2010 before Florida mandated E10, I used to get 500-550 miles a tank, getting 22mpg in my V6. Now I see 18 if I'm lucky.