The German database of 100.000's of cardrivers logging their fuel consumptions is a good place to start.
Here theres enough cars to getting a real picture of a cars fuelconsumption. Some hypermile, some dont.
For my car, the 1.0 liter Yaris 1 from 2000, the avarage form 133 cars is 6,07 liter pr. 100 km.
The best - a real hypermiler is down to 4,32 liter pr. 100 km.
Try to go and have a look. Heres a whealt of usefull information of what a given car acturlly use in fuel in everyday life - not some calculated numbers.
Might also be of good use when looking for your next car.
Mileage Calculator and Vehicle's Costs Analyser