Normal - how quickly and easily it goes up to the 20 and above mark depends on the car. The 330i goes up and over 20 very easily compared to my Wife's 320i, but in reality both cars use about the came amount of fuel overall. Of course, once you settling at cruising speed it's fine again, and what goes up must come down - so slowing down or going down the hill that you have climbed results in possibly a 0 l/100 km consumption, so this balances out in the end.
With my car I always try and "keep" the econometer south of the 10 l/100 km when cruising or maintaining speed and it's amazing how you can learn how best to keep your car's economy down based on this and changing your driving style to best suit the car's characteristics.