I have no scientific evidence to support this theory, however here goes. There are more cars in Doha with the filler cap on the left (drivers side) than on the right side (passenger side) of the car.
My car has the petrol filler cap on the right side. Although I have the inconvenience of leaning across to pay the attendant, the longest queues are most often to the lines where the filler cap is on the drivers side of the car. Check this out for your self when you’re driving by.