WWJD08, I had posted originally that the Prius with the top down was getting better mileage than top up but after another 1200 miles, the convertible gets 44.6 on freeway on recent round trip to Prius meet in Orange County (100 miles or so) and top up, maybe every so slight increase to 45. Around Los Angeles on side streets though 40 with top down but steady 40. Hardly ever have the top up. Best, Exproducer