Ahhh... Not sure where you pulled those figures from ejectx3. On a BNE-ADL 737 flight plan from today the cost to carry is actually 48kg per 1000kg. Or 480% more than you suggest. To carry 2 hours extra fuel would cost closer to 230kg of fuel rather than 40kg. Then as ozbiggles suggests, if you multiply that across every sector then said insurance is a LOT more costly than you suggest.