This article focuses on institutional change in the German gas market driven by EU internal market and climate policies. It argues that institutional change has functional externalities for energy security. The German gas market provides a useful case study, as Germany is the biggest continental gas market, a major hub and transport country which has largely privatised, unbundled and separated its natural gas undertakings. Transition is ongoing, tending towards an internal market. Inter/national natural gas economics is in flux. Institutional evolution has repercussions for corporate and market structures, the operating of the system and the realization of transactions. Changes in the institutional framework crucially affect energy security, which is often associated with institutional stability. On the basis of this case study, it is argued herein that the security of natural gas supplies should be reexamined in the context of the developments described above, since overall the institutional changes in natural gas security lag behind the EU's internal natural gas market development. (C) 2014 Elsevier Ltd. All rights reserved.