In supply chains of petroleum industry, maintaining a proper inventory level for multiple petroleum products is a crucial issue. Basically, this chain has several elements like producer bases, consumer bases and terminals that are linked by means of a multi-modal transport network. These elements must cooperate to achieve the global goal of the system with a minimized cost. To achieve this goal, this paper presents a multiagent protocol for simultaneous negotiations based on the Contract-Net and the application of this in the chain aforementioned. As a result, this protocol proved to be very efficient to return a feasible solution in a low processing time.