E10 gasoline in our old school engines.

[Dead Parrot]

In OKC, pure gas is fairly common but is more expensive then E10. I run the E10 since there isn't much difference in mileage on mine. By math, E10 has about 97% the energy of pure gas of the same octane. Not going to be noticeable on a vehicle that gets 13 MPG @ 70mph on the highway. E10 does seem to be bad for small engines even if they claim to be rated for it.

All things being equal, adding ethanol should raise the octane a bit but I think most of the refineries compensate by blending the ethanol with lower octane gas to arrive at the proper number.