In international commercial arbitration, the parties to the dispute are free to select the law that governs the substance of their dispute; provided that the chosen law is not contrary to the public order and peremptory norms. In case the parties have not chosen the law, which governs the nature of the dispute, the dissention arises. The absence of the selection of the applicable law governing the dispute slows down the arbitration process. In this case, the "arbitrator" must determine the law according to which the nature of the case is heard; due to the involvement of an international body in the dispute and the silence of the parties, the law governing the nature of the dispute is not clear from the beginning. Based on what is mentioned above, the "arbitrator" confronts several options which are discussed as the approaches in this research paper; meanwhile, the orientation of the countries and the arbitration organizations towards the approaches included the restrictions of such selection is examined. This article, while conducting a comparative study with the library method, relies on the assumption that the arbitrator has the same will as the parties in choosing the law that governs the nature of their dispute.