Thanks Faisal. I'll take it up for computerized tuning and see the difference.
Xulfiqar, my drive is mostly on Sh-e-Faisal and Clifton. Thus, not much crowded as MA Jinnah road or I.I.Chundrigar road.
The process of calculating mileage is that I fill up the tank with 10l of petrol upon lighting-up of the 'yellow' light indicator showing less fuel till the next time it lits up again and see the total mileage covered. It covered exactly 69.5 kms in 10 liters of petrol with AC.
Fyi, the car has 195/65/15 Michelin tyres. Thus, do not see major effect due to these.
I don't smell any petrol but wonder if there is any minor leakage or possiblity of fuel evaporation???
Thanks for your help and looking for more.
May Almighty Allah help to immediately fix up this petty issue - aameen.