sali2002, the car is EFI
Yes, I know that CNG prices have increased that's why I didn't talk in terms of what cost I am incurring for fuel. I talked in terms of the number of kilometers the car goes in one filling.
aridsoul, I know the capacity of khyber was different. It gave me over 200 kilometers for a 50L cylinder. According to this, it was giving me 4 km per L of CNG. Using the same calculations, I would have assumed that my Santro would give me 168 km to one filling. It should be giving ever more because it is EFI and khyber isn't.