The multilateralization of international investment law cannot be observed only from the perspective of foreign investors that are able, through the operation of MFN clauses, to rely on uniform rules governing their investment activities in a specific host State. The convergence of bilateral treaties into a multilateral investment regime also becomes apparent from the compliance perspective of States. Even absent the operation of MFN clauses, and even though the bilateral structure of investment treaties would in principle allow for differentiated treatment depending on the investor's national origin, host States are increasingly troubled in applying differentiated treatment to investors from different home States. Instead, compliance with investment treaties, in practice, increasingly resembles compliance with obligations under a multilateral regime as a uniform level of treatment of foreign investors is required of States.

Multilateral regimes are characterized by the existence of identical obligations of one State vis-à-vis at least two other States. These obligations can be either erga omnes and owed to the international community as a whole, or erga omnes partes (or inter partes), that is, owed independently and individually to every participant in a multilateral regime. While the difference between erga omnes and inter partes obligations relates above all to the question of who is entitled to enforce these obligations in case of their breach – either every single participant in a multilateral regime in case the obligation is erga omnes, or only the individual member that has been harmed by a violation of the obligation in an inter partes relationship – the differences are marginal from the perspective of the addressee of the obligations.