Lots of states mandate E10 and it isn't a problem to run it on most vehicles. E85 should be run ONLY in vehicles designed for it. Flex fuel vehicles direct from the mfg and vehicles that have undergone a conversion to allow it.
Fuels with enriched blends Ethanol will get less MPG compared to pure gasoline. Gasoline has 104,000 BTU/gal, E10 has 100,700 BTU/gal, and pure ethanol has 70,300 BTU/gal. Various estimates say vehicles with using the E85 blend will get 15 to 25% lower MPG.
Ethanol contains less energy than gasoline, so ethanol blends get fewer miles to the gallon. Ethanol advocates may make the claim that the drop is 2 percent or less for E10 but Iowa State University Professor Larry Johnson and other independent testing estimates that E10 delivers 96.4 percent of the miles per gallon of gasoline, a drop of 3.6 percent, and E85 delivers only 80 percent.
Based on numerous studies, a vehicle that gets 25 miles to the gallon (yea, not our XJs) and has a 17-gallon tank could go 425 miles on a tank of pure gasoline. That same vehicle would get 24.1 mpg with E10 and travel 410 miles, or get 20 mpg with E85 and go 340 miles.