Maybe what needs to be specified, some of the reasons to tanker fuel:1: Total Trip cost reduction. Self Explanatory. By purchasing and carrying as much of the cheap fuel, you reduce having to use the expensive fuel. Over the total trip, the cost is less. This assumes you know the price per gallon at departure and destination airports and can actualy control the amount of fuel purchased. 2: Safety: Taking that extra fuel to eliminate putting a plane in the water, having to turn around midway, Island fuel reserves come to mind...the more fuel you have the more time you have. And more I am sure...But for the purposes of this thread, the question seems to be, when does it start costing money to carry extra fuel around....Since it's obvious that carrying one once over minimal legaly required reserves cost money to carry to the destination, the question remains for those agonizing over carrying tankered fuel: How much safety are you willing to give up, inorder to save a buck for the company?