Originally Posted by germ
Agreed. Lots of misinformation. There is no difference in energy content between different octane grades, so I don't believe there will be differences in mileage.
Premium fuel gets better gas milage because the higher octane allows the engine to advance timing because it doesn't see knock as early. This inproves the efficiency of the engine and equates for slightly better gas milage as a result, tho it is not much, maybe 1 mpg if that. Likely the OP is just seeing a random sample that is higher than his average.