*This period of time is doubled in an international arbitration (art. 5(2)).

5. If and to the extent that the lists which have been retur­ned show an insufficient number of persons who are acceptable as arbitrator to each of the parties, the Admini­strator shall be authorised to invite directly one or more other persons to act as arbitrator. The same shall apply if a person is not able or does not wish to accept the Administrator's invitation to act as arbitrator, or if there appear to be other reasons precluding him from acting as arbitrator, and there remain on the lists an insufficient number of persons who are acceptable as arbitrator to each of the parties.

6. If the arbitral tribunal is composed of three arbitra­tors, the arbitra­tors shall choose a chairman from amongst themsel­ves, if necessary, in accordance with the provisions of arti­cle 16(3).

7. If the parties agreed only to the appointment of arbitra­tor(s) by the NAI, without referring to arbitration by the NAI or arbitration in accordance with the NAI Rules, such appoint­ment shall take place in accordance with the provisions of