Obviously, the Prius is noteworthy not because of its powerful engine -- its accelerations won't ever rivet you to your seat -- but because it is supposed to use little gas. Anyway, after three weeks of driving, today it alerted me through a blinking square on the dashboard that it needed a refill. When I brought it to the gas station, her odometer was showing 670 km. Her tank was full after drinking 41.25
liters of unleaded gasoline, which brings me to my main point.
Assuming the gas tank was completely full when I got it (which is somewhat an iffy proposal), my Prius yielded an average of 6.1 liters for 100 kilometers. By the way, 6.1 l/100km is equivalent to 38.56 MPG (US gallons). This result is considerably worse than the mileage advertised by Toyota, i.e. 4.4 liters per 100 kilometers, i.e. 53.46 MPG. Nevertheless, the Prius still emerges as being more fuel efficient than most other cars.
Of course, a single measurement is not necessarily representative, especially considering that those 670 km included a drive to a nearby mountain. After googling for a few minutes, I stumbled upon a US-governmental page showing the MPG obtained by other drivers . My MPG happens to be worse than the average shown on that page.
The second time around, I measured 810 km for 42.02 liters of unleaded gasoline, or 5.2 liters per 100 km (45.3 MPG). This result is very much aligned with the average reported by other drivers. It could probably be improved, as the 810 km included a trip to a nearby mountain.
The difference with the first result can be explained by the fact that on the highway I now drive a little lower than the authorized limit, at 110 km/h instead of 120km/h.