First off all, I do not ride my Burgman 650 to get the best fuel millage, but after 11,000 milles, I made some interesting finds. For the first 5,000 milles i ran with regular 10W40 OEM oil in motor, CVT and 80W90 Castrol in the final drive. All that time i would fill with regular, keep my numbers and made and average mpg, i would run the bike for 3 tanks of regular.and 3 tank of high test, each time i'd get 2 more milles to the gallon with high octane,always ride the same road for commuting.The real good thing came when,I switched to all synthetic oils, on the spot got 3 more MPG, now this is personal,But for myself,I know that with the best stuff my Burgy give me peak economy and peak performance. I now average 50 mpg all the time.Just my 0.2 cents. JAYPE.