Section 18(6)(b) in The Appellate Tribunal for Petroleum and Natural Gas (Procedure, Form, Fee and Record of Proceedings) Rules, 2009
(b)The numbers of the parties shall not be changed and in the event of the death of a party during the pendency of the appeal or petition or application, his legal heirs or representative, as the case may be, if more than one shall be shown by sub-numbers.