If you go on a long cross country trips, you're bound to get a mix of gasolines with and without ethanol. I find ethanol blends, which are prevalent in California, yield about 10% less mileage than normal gasoline.
Ethanol in gas is also very prevalent in Oregon and Washington (actually required by State Law). Ethanol is higher octane than gasoline but contains 30 percent less energy, so a 10 percent ethanol blend will result in a net energy loss of 3 percent. We have a few stations in the area that sell non-ethanol premium and I try to use non-ethanol gas whenever I can but I haven't seen much of an improvement in gas mileage even when I use the non-ethanol.
During my trip I stopped at several stations in South Dakota and Montana that were adding 10 percent ethanol to 87 octane gas and calling it 89 octane super unleaded...and charging a dime less per gallon for the "super unleaded". Those stations usually did not sell premium gas.