The capacity of the transmission network determines the extent of integration of a multinational energy market. Cross-border externalities render coordination of network maintenance and investments across countries valuable. Is it then optimal to collect powers in the hands of a single regulator? Should a common system operator manage the entire network? I show that optimal network structure depends on (i ) how the common regulator would balance the interests of the different member states; (ii ) how the gains from market integration vary across countries; (iii ) network characteristics (substitutability versus complementarity); and (iv ) the social cost of operator rent.