Originally from International Arbitration Checklists - 3rd Edition

The Number of Arbitrators

The first thing to consider is whether the case is best handled by one or three arbitrators.   This evaluation should take place when the dispute arises, regardless of whether the arbitration agreement already specifies a number. It may well be that both sides will agree that while the arbitration agreement provided for three arbitrators, the matter is one in which a single arbitrator will be sufficient.  The situation may also arise where the parties agree that three arbitrators are appropriate, even though the arbitration agreement specifies one. 

There is much to be said for a single arbitrator, including lower cost, efficiency and ease of coordinating dates and hearing times.  A single arbitrator may also be prepared to make a hard decision without his conclusion having to be softened or watered down in order to please the majority.  On the other hand there is a danger, particularly in large, complex cases, that if the single arbitrator gets it wrong there is no appeal.  For this reason, as well as cultural or business sensitivities, most international arbitrations have three arbitrators.

If the arbitration is ad hoc and the arbitration agreement does not specify how the single arbitrator is to be chosen, it is usual for the person commencing the arbitral process to provide to the Respondent a list of candidates who would be acceptable to the Claimant, usually with a short biography of each.  This is of course subject to any rules the parties may have previously agreed to.  It is the usual procedure that a short but realistic period of time is then set within which the Respondent must agree to one of the names.  If the Respondent does not accept any of the candidates, a new list can be provided by either party.  If no agreement can be reached, the court at the place of the arbitration (presuming no arbitration institution becomes involved), has the power to appoint the arbitrator upon the application of either party. 

In some ad hoc arbitrations the arbitration agreement will provide that an independent authority is to appoint the arbitrator.  For example, the arbitration agreement might require that a sole arbitrator be appointed by the President of the IBA.