It might be enriched ethanol blend.
Here in Iowa and Minnesota, some stations sell 100+ octane that is 80-90% ethanol.
And it’s usually as cheap as regular gas - $1.80/gal.
Just remember that octane is not a rating of power, rather it’s a rating of the ability to burn. I.e. high number = easier to burn.
Also, ethanol has a lower power by volume factor than plain gas. Your engine will not miss but you will get less miles per gal.
FYI, diesel has the highest of common fuels: approx 160k btu/cc vs 140k btu/cc for gas.