Previously I had Vitz 2004 with CNG, the best it gave me was 175Kms on highway without AC and the worst it gave me was 95 Kms in city without AC in one full cylinder of 8KG
Now I have vitz 2006 1.0 ltr Petrol and the best it gave me on Lahore to Multan road was 20Km/l in which from Lahore to sahiwal it was on AC. the worst it gave me was 10 Km/L in city with AC
My observation of three years experience with vitz is that following things effect the fuel average:
1- RIM Size (bigger the tire size means lesser the average, you can get best average on only the size for which the car has been designed which is 14")
2- Tyre aspect ratio (don't use too broad/wide tires, though they increase road grip but badly effect on fuel economy)
3- Driving style (aggressive = lesser AVG, smooth and calm = good AVG)
4- Petrol Type (Don't use PSO Petrol, and try to get your tank full at once from a good/running pump)
5- proper maintenance (change the oil filter, oil, air filter after 2500 to 3000 Kms Max and use only recommended oil, don't change the brand or type of oil every time, just select a good oil and try to carry on with it. I use ZIC which is good for new engines but not good for engines with mileage above 100K)
6- And finally it also count that how much extra weight you put on your car...more persons mean more power required which mean more fuel consumption in lesser distance;)
Cheers