Thanks for your reply.
I believe I did not make myself clear enough, I will try once again.
I know how to visualise the social costs and their sub-components, as well as to drawn the boundaries of the costs calculation.
I calculate the social costs for the entire system.
When visualising the different components of these costs, I noticed that the resources costs (at the costs: fuel imports and costs:fuels exports), are not those I was expecting. Since my country is a fuels exporting country, that my exports are much higher than that of the imports and that my imports and exports costs are the same, I was expecting that my costs: fuels exports results be higher than the fuels: imports.
I couldn't spot my mistake if any. For me, logically at this branch, the costs should be calculated as follow: import Costs x resources imported and exports costs x resources exported. If this is the case, so I should find at the "resources costs" that my exports benefits are higher than my exports costs.
I went through the different posts and re-reads the user guide and the training material but I couldn't find a clear answer to my question (how the imports and exports costs are calculated and why my exports benefits are lower to the imports costs while it should not the case).
Thanks for your help
Nadia