It's been proven that the screen in the car reads 3-4 mpg high. (US at least) Mine has mostly read 35-38 mpg but when manually calculated it ends up being 32-34. Here's all of my fill ups since I bought the car:Are you guys going by the on-board mileage readout? Because according to mine I've been averaging around 37-39 mpg highway and low 40's when on a side road holding an even 80 km/h.