In our company we periodically get a list of sectors on which Tankering is recommended. It lists the total cost savings per kilo-litre of fuel.
This includes not just the price difference between fuel at departure and destination, but also factors in the approximate expenditure (extra fuel burned) incured in carrying the extra tankered fuel.
The net figure is provided in the list, and it is plain to see the immense cost savings involved in tankering on certain sectors.
The extra fuel burned to tanker the extra fuel is minimal as compared to the savings from the difference in cost of fuel at an expensive destination.