Good petrol pumps (gas stations for my friends from an earlier life) are hard to find in Karachi. Good petrol pumps that will give you consistent mileage weeks after weeks are even harder.
After painfully experimenting with almost every brand and every locality I have now built my own list of three pumps that I use for topping up my fuel tank. Not surprisingly all three of them are Caltex pumps. After being a loyal shell customer for about 3 years I gave up on Shell when fuel prices sky rocketed in 2008 and it was obvious that there was something really dark going on at most Shell Petrol Pumps. The average difference between Shell and Caltex is 60 kilometers of mileage on a full tank. This after carefully tracking my consumption for the twelve months. At 8 rupees per kilometer that is about 500 rupees for every top up, 2000 rupees in your fuel bill for every month if you drive as many kilometers as I do in a good week.
About a year ago I switched permanently to Caltex. When caught in a bind, I will do PSO, but generally I will stay as far away as possible from a Shell pump. The pumps on my list are the Caltex pump on University Road immediately after NIPA (the one after Civic center is a no no), the Caltex at the do-talwar roundabout, and finally the Caltex just after YMCA and just before NAPA in the city. All three have been giving me 360-370 kilometers on a 40 liter topup over the period of comparison. Some of the pumps on my swine list have only been able to do 290-300 for the same amount of fuel.