In this article authors study an analyse the rationale underlying the arbitral awards rendered under the Energy Charter Treaty (ECT) dealing with the criteria to adjudicate and determine the damages in case a breach of the Treaty has been committed by the Member state. Additionally, investment arbitration precedents are also being considered to determine whether there is an International Public law principle establishing the most appropriate method to calculate damages. Finally, a similar analysis is carried out as regards time limitation defences to bring claims against a State under the ECT.