Brothers, let me ask 1st that whats the average of alto on petrol????
mostly it gives 8 to 10KM right? max 11-12km per litre....
Same was the issue with me when i bought mine around 6 months back, it used to give me max 10 - 11 km per litre....and that too with light foot. but after that i have changed engine oil to Liquimoly, (check my previous post), it now gives 500+ KM in a full tank in city drive 
Thanks to Liquimoly, it really improved average fuel consumption of my car.
I Highly recommend (H)