Often the oil company controls all three levels, that is it refines, distributes and then sells to the customer. I have always said that, when a service station closes down and a self-serve gas bar opens, that is because the oil company is operating it.
Souvent, en plusieurs endroits, la compagnie pétrolière détient le pouvoir sur les trois, c'est-à-dire qu'elle raffine, elle distribue et elle fournit le service aux clients.