In liters per 100 km.

Here are some example with european city cars :

Ford Fiesta 5 [9600€] - theory : 3.6, reality : 4.7 (+1.1)
Hyundai I20 (2nd Generation) [12900€] - theory : 3.8, reality : 4.8 (+1.0)
Seat Ibiza 5 SC [8900€] - theory : 3.8, reality : 5.2 (+1.4)
Toyota Yaris 3 [8900€] - theory : 3.5, reality : 5.5 (+2.0)
Seat Leon 2 [11400€] - theory : 3.8, reality : 5.6 (+1.8)
Peugeot 208 [8900€] - theory : 3.8, reality : 5.6 (+1.8)
Renault Clio 4 Estate [11400€] - theory : 3.3, reality : 5.8 (+2.5)
Peugeot 2008 [14200€] - theory : 3.8, reality : 5.8 (+2.0)
Dacia Sandero 2 [8900€] - theory : 3.5, reality : 5.8 (+2.0)
Citroen DS3 [11300€] - theory : 3.8, reality : 5.9 (+2.1)
Volkswagen Polo 5 [9900€] - theory : 3.8, reality : 6.0 (+2.2)
Citroen C3 (2nd Generation) [8900€] - theory : 3.8, reality : 6.0 (+2.2)
Hyundai I30 (2nd Generation) [13900€] - theory : 3.8, reality : 6.1 (+2.3)
Renault Clio 4 [9600€] - theory : 3.6, reality : 6.6 (+3.0)
Opel Corsa 5 [13900€] - theory : 3.3, reality : 6.7 (+3.4)
Clio 3 [14500€] realité - theory : 4.9, reality : 7.5 (+2.6)

You can check by yourself in the different forum dedicated to autombiles.