I have a 2014 Prius I just finished a test between E-10 and E-0. I ran 3 tanks of E-10 and got 54.65 mpg. Then I ran 3 tanks of E-0 premium(only ethanol free available) and got 55.97. So in this car I only got a bump of 2.4%. Previous tests on a 2012 Camry Hybrid and a 2008 Corolla yielded a much bigger jump, around 6 to 8 %. Since the E-0 is 20 cents or about 6 to 7 % higher in cost per gallon, I will not be using E-0 any more on the Prius and I stopped using it a few months ago on the Camry.