Every mandatory E10 state has exemptions to their blending law, because there are a number of piston engine applications that should not, and some that cannot, use ethanol blended gasoline. Unfortunately the exemptions are not uniform. They vary from only one exemption in Washington, aircraft, to a universal exemption of premium unleaded in Missouri. All states exempt aircraft usage, but most states like Oregon and Washington make it almost impossible to get unblended gasoline. Oregon is the only state that allows for unblended regular and premium gasoline for the exemptions, and then makes it almost impossible to get any unblended gasoline. All other mandatory ethanol states just allow clear premium unleaded gasoline for the exempted classes.
The following piston engine applications should not use ethanol blended gasoline: