Risks associated with selling petroleum products through a commodity trading bustiness

1- What are the risks associated with selling petroleum products through a commodity trading bustiness and how they can be managed, reported and controlled.
2- What are the benefits of trading petroleum products via a trading company instead of it to be via the original producing petrol company directly.
3- Compare between the risks of two commodity companies which are Trafigura and Total and how they manage it.
Please include graphs, charts and tables.