...and up to 10% ethanol I believe. But: Ethanol is hard on the rest of the fuel system, and while the current tanks are supposedly ethanol-resistant, several horror stories are out there about fuel system contamination when running ethanol. There are others who have run hundreds or thousands of hours with ethanol fuels with no ill-effect.

Then there is the issue of vapor pressure. Mogas vaporizes much more quickly, leaving it's additives behind. You can't let it sit like you can with 100LL.

So if you have access to 91 octane ethanol free fuel, and burn it regularly, it's your best option. But for many (most?) It isn't practical.