Ok, here is my experience. My I10 is almost 3yrs old(2008) and last week I went ooty. I got a satisfactory performance of 18.8km/l in over all trip(250km hill, 600km high way). I started from Bangalore and measured the fuel consumption by tank full-to tank full procedure. It took 45lit to cover 850km. Hence the mileage I got 850/45 = 18.8km/l
However, I have obeyed strict rules to get max mileage
Pumped up Tyre 33psi.
I have not crossed speed limit 80 (i.e. 2000 rpm).
Did not rest my foot on clutch.
Used neutral when getting down from hills.
accelerated the car gradually to reach 70-80.
I though this can be helpful for guys going for long drive. However in city I get 13-14km/l. I hope this post will be helpful.