(a) Where three arbitrators are to be appointed and the parties have not agreed upon an appointment procedure, the arbitrators shall be appointed in accordance with this Article.
(b) The Claimant shall appoint an arbitrator in its Request for Arbitration. The Respondent shall appoint an arbitrator within 30 days from the date on which it receives the Request for Arbitration. The two arbitrators thus appointed shall, within 20 days after the appointment of the second arbitrator, appoint a third arbitrator, who shall be the presiding arbitrator.
(c) Notwithstanding paragraph (b), where three arbitrators are to be appointed as a result of the exercise of the discretion of the Center under Article 14(b), the Claimant shall, by notice to the Center and to the Respondent, appoint an arbitrator within 15 days after the receipt by it of notification by the Center that the Tribunal is to be composed of three arbitrators. The Respondent shall appoint an arbitrator within 30 days after the receipt by it of the said notification. The two arbitrators thus appointed shall, within 20 days after the appointment of the second arbitrator, appoint a third arbitrator, who shall be the presiding arbitrator.
(d) If the appointment of any arbitrator is not made within the applicable period of time referred to in the preceding paragraphs, that arbitrator shall be appointed in accordance with Article 19.