Regionalism and Overlap in Investment Treaty Law: Towards Consolidation or Contradiction?

States increasingly conclude intra- and inter-regional treaties to protect foreign investment. In many instances, these regional treaties will overlap with existing bilateral investment treaties. This article finds that every fourth bilateral interstate relationship is affected by such overlap. Only few states use regionalism to de jure or de facto consolidate their investment treaty network. Most countries opt for parallel bilateral and regional treaty layers. Such overlap raises coordination challenges as parallel treaties may duplicate or contradict each other increasing the risk of parallel proceedings, double jeopardy, and normative conflict. As these challenges are not specific to investment law, and also exist in trade law, states should draw from both fields in order to develop solutions. By using a comparative perspective, this article identifies new areas for cross-fertilization between both disciplines and offers guidance on how best to manage vertical treaty overlap arising from regionalism.