Between purpose and fragmentation: contemporary issues of “res judicata” in international investment arbitration

Abstract

Res judicata plays a structural role in international investment arbitration, as it guarantees the stability of final decisions, prevents conflicting awards, and preserves the legitimacy of the system. However, the proliferation of forums, jurisdictional titles, and judicial seats has multiplied the scenarios in which this principle is invoked, often with divergent outcomes, thereby threatening the stability and legal certainty of arbitral awards.This article critically examines the foundations and effects of res judicata in investment arbitration, its interaction with related doctrines such as lis pendens, fork-in-the-road, abuse of process, and estoppel, as well as the relevant jurisprudence of ICSID, UNCITRAL, and ICC tribunals. The analysis is based on a comparative approach to the main regulatory frameworks worldwide and to national rules applicable to international arbitration, while also considering studies such as the Final Report on Res Judicata and Arbitration by the International Law Association (ILA) and the more recent Report on Res Judicata in International Arbitration by the International Bar Association (IBA).