I'm with A4 on this !
Many here will be familiar with their PLOGs telling them that their jet aircraft (typically) burns 4% of every ton of fuel onboard just to carry that fuel on a per hour basis.
Nb. A ton of JetA1 kero roughly costs about $200.
So if one was to say that you average trip was four hours long and in order to arrive with an extra ton of fuel at your destination ( that would provide about 25 minutes of extra flight in a B737 ) one would need to load on .......... click click tap tap......... 1.17 tonnes of extra fuel, i.e. 1170 Kgs over the FlightPlan figure. E.g. :
In the 1st hour you'll burn 4% of the extra 1.17 tonnes, so giving 1.125 tonnes extra.
In the 2nd hour you'll burn 4% of that, so giving 1.080 tonnes extra.
In the 3rd hour you'll burn 4% of that, so giving 1.040 tonnes extra.
In the 4th and final hour (of your averaged 4 hour flight) you'll burn 4% of that and arrive overhead the runway at your destination with 1 tonne of extra fuel (over the PLOG figure - all things being equal, so to speak).
So, to arrive with one tonne of extra fuel you've had to burn 0.17 tonnes of the stuff ( 170Kg's )
That equates to an average total cost of $35 ( or $8.75 per hour - and where a B737 typically cost $100 per MINUTE to operate ) - including discounting as 'averaged' any disparity in fuel uplift charges from the departure airports, in that you'll always have an extra tonne in the tanks.
Q). So what does it cost to divert ?
A). Lets say about $3500.
Which if you put that into perspective means that it would take about 100 normal sectors (assuming that they are 4 hours long) with no diversions ( as you're carrying that, oh so lovely, extra tonne which often proves enough to save your sorry ass ) to cover the 'direct' costs of just one diversion - to say nothing of the intangible costs.
Or that alternatively for the cost of $3500, spread over 100 flights, you will never have to divert ( a simplistic argument I know ).
Now nobody is saying "Fill the wings and put the trip fuel in the centre", but the cost of fuel tanking (or not) policies do need to be seen as part of the bigger picture and include airmanship, rather than brinksmanship !
But as is oft said, "Go figure !"