Unbundling vertically integrated energy companies with the goal to spin-off and neutralize (transmission) system operation lies at the heart of the Third Package of European energy legislation, and namely Directives 2009/72/EC (electricity)1 and 2009/73/ EC (gas).2 The tug-of-war for an appropriate unbundling model also determined the public and academic debate at the time. This is not the place for yet another account of the evolution of the unbundling rules.3 Three different options were finally included in both the Electricity and Gas Directives.