You will get better fuel economy with a 10% ethanol, 90% gasoline mixture versus a pure100% gasoline mixture. There is a notion out there that using a mixture of gasoline with ethanol will provide better gas mileage. The idea that ethanol is a cleaner burning fuel has given rise to the idea that it also improves your fuel economy. This is not true.
In fact the energy output for ethanol when it is combusted is less than that for gasoline. This means that for equal parts of ethanol and gasoline the gasoline burning mixture will provide more energy to your vehicle than ethanol would. So you are getting reduced fuel mileage when using a 10% ethanol gasoline mixture at the fuel pump as compared to a 100% gasoline mixture. Unfortunately in this day and age the majority of gasoline pumps are mixed with 10% ethanol. So we are all experiencing reduced fuel economy across the board. Unless you happen to find a gas station that does not have ethanol mixed in with their gasoline you are out of luck here.