The multilateralisation of regionalism takes different forms when applied to deep versus shallow regional trade agreements (RTAs). Shallow agreements focus on discriminatory tariffs; hence, multilateralisation strives mainly to reduce discrimination. Deep agreements focus on the disciplines necessary to foster international production sharing; key provisions often resembling unilateral liberalisations that just happen to be bound by an RTA. In this case, multilateralisation achieves network externalities and solves co-ordination problems. This paper suggests a novel framework for thinking about the costs and benefits of multilateralising the provisions in deep RTAs, including those that seem set to appear in the Trans-Pacific Partnership (TPP) and the Trans-Atlantic Trade and Investment Partnership (TTIP).