An arbitral tribunal (or arbitration tribunal) is a panel of one or more adjudicators which is convened and sits to resolve a dispute by way of arbitration. The tribunal may consist of a sole arbitrator, or there may be two or more arbitrators, which might include either a chairman or an umpire. The parties to a dispute are usually free to agree the number and composition of the arbitral tribunal. In some legal systems, an arbitration clause which provides for two arbitrators (or any other even number) is understood to imply that the appointed arbitrators will select an additional arbitrator as a chairman of the tribunal, to avoid deadlock arising. Different legal systems differ as to how many arbitrators should constitute the tribunal if there is no agreement.