Large scale and transnational electricity grids facilitate balancing capacity across the areas that they serve and increase potential for energy trading. Offshore grids and the more ambitious notion of supergrids are beginning to play a significant part, especially in Europe, in the realization of improving security of domestic energy supply and expanding renewable energy production. As such, offshore (super-) grid development provides an excellent example of the move towards marine regionalization. Moreover, because of limited spatial claims and environmental impacts, marine electricity systems seem well-aligned with the rationale of ecosystem-based management, which is at the heart of European marine governance. By outlining their historical path and the envisioned outlook, in this article we show how offshore (super-) grid developments link up to marine regionalization and its related processes of integration and cooperation. It is argued that scaling-up grids to the level of regional seas is not unproblematic, but faces obstacles which depend on persistent practical and policy realities, and which may be relevant to other expressions of marine regionalization.