Ethanol

Ethanol is an alcohol-based fuel produced by fermenting and distilling starch crops (corn, barley, wheat, etc) after they have been converted into simple sugars.  100% ethanol is not generally used as a motor fuel, instead, ethanol is used as an additive to give benefits to unleaded gasoline.  These benefits include lower costs, higher octane ratings, and lower emissions.

The two most common blends of ethanol gasoline are:

E10 - 10% ethanol and 90% unleaded gasoline

E10 (sometimes called gasohol) is approved for use in any make or model of vehicle sold in the U.S. and adds 2-3 points of octane to gasoline. 

E85 - 85% ethanol and 15% unleaded gasoline

E85 is an alternative fuel for use in flexible fuel vehicles (FFVs).  This blend contains approximately 27% less energy per gallon than conventional gasoline, but typical burns more efficiently.