My Jazz when new was giving really bad mileage, until about 2,000KM on the odometer, but as it's aged, it's really settled down. A friend consistently gets 5.0L/100KM, I consistently get 5.5-5.7L/100KM, and have done the maths.

North Brisbane to Gold Coast return 5 times (1 return per day, approx 125KM in each direction, totalling 250KM) was giving me 5.2L/100KM, running at 110KHM, just over 3,000RPM

I estimated a 42L tank could potentially travel 800KM, but that would be absolutely running the trank dry (they're not THAT heavy to push, right?)

Two important factors :
1. an un-modded 1.3L iDSI motor
2. Standard grade 91RON unleaded fuel

Cheers,

Blip.