Ethanol has less enegry than octane, so it takes more to do the same amount of work. I use 93 octane and found a 10% increase in MPG for less than a 3% increase in cost from 89 octane. The Exxon web site has a map of the US that shows where they use oxgenated (ethanol) agents in their fuel, and in most of the US they don't. I always use Chevron, Exxon, or BP. My milage is great.
http://www.exxon.com/USA-English/GFM/Files/US_Gasoline_Map.pdf
