Since the early 80s in Illinois it's been 10%. I had a '79 Mustang 4 cylinder with a carb that knocked like crazy but the E10 fixed it.Sometimes I wonder how I've gotten 31 years out of my Toro lawnmower, 24 years out of my lawn tractor and nearly as many years out of my string trimmer and chain saw when all we've had here in Southeastern Wisconsin is oxygenated fuel. All of this attacking of parts must occur elsewhere?