Although
very few states still—or ever did—mandate ethanol in gasoline, ethanol-blended gas is widely available; indeed, it can be difficult to find an ethanol-free gas station (if you want to find one near you, try
this resource).
The blend wall—the percentage of ethanol to gas considered safe for car engines—is 10% or E-10, and past efforts to create and push E-15 have failed. The little-known practice of
automakers quietly voiding warranties on cars whose owners use E-15 gasoline illustrates the industry's understanding of the harm that levels of ethanol passing the blend wall (E-10) causes to car engines.
Triple A also warned against the use of E-15 gas in pre-2012 cars. Not only are engines—cars, boats, lawn mowers, chain saws, etc.— harmed, but ethanol blended into gasoline, not just the higher E-15 blend but even that at the blend wall, also contributes to
a loss of mileage.
The percentage of ethanol to gas has been increasing relatively steadily over the past decade as indicated by
this graph from Bloomberg: