... a station owner gauges his tanks with a long stick and knows how much gasoline to order. The truck usually has multiple compartments (for each grade + Diesel) and the truck only 'tops off' the tanks. When the truck leaves there is still plenty of room in the tanks. The reason a station does not run his tanks FULL is because next week the prices may drop and he can't buy and because he has no where to put it. If gas drops he buys a little 'extra' and his AVERAGE costs per gallon drop a little.... more money in his pocket, remember his kid in college? You do the same thing if you know gas is going up, you fill up before it does. So does the station owner, he ain't stupid!