Fuel economy is lower when E85 fuel is used because ethanol has lower energy content than gasoline. 

According to the National Ethanol Vehicle Association, use of E85 in Flexible Fuel Vehicles results in "a 10-15% drop in fuel economy. This will vary based on the way one drives, the air pressure in the tires, and additional driving conditions." 

Since E85 may be lower in price than regular unleaded, cost per mile may be similar.  E85 is generally priced to be competitive with regular 87 octane unleaded gasoline.  Tax credits received by fuel blenders may make the cost of E85 significantly lower than regular unleaded. 

Executive Directive No. 2005-4, as part of the promotion of energy efficiency in the state motor vehicle fleet, directs:

As the public Alternative Fuel infrastructure continues to develop, require the users of motor vehicles within the state fleet to refuel with Alternative Fuels to the extent feasible.  Where Alternative Fuel is available and cost-effective, require users of motor vehicles within the state fleet to purchase Alternative Fuel.

All drivers of state E85 vehicles are encouraged to support alternative fuels by fueling with E85 whenever possible.