The gas and electricity markets in the EU were characterized largely by state-owned or state-controlled, vertically-integrated undertakings with monopolistic or oligopolistic market positions, operating on the basis of long-term gas supply contracts, centrally-planned investments in transmission networks and energy supply. Following the initiation of the single market initiative and liberalisation agenda, EU energy law and regulation now require inter alia third party access to networks and ownership unbundling. Although traditional long-term supply arrangements could be seen as a means of guaranteeing sufficient gas and electricity supply at reasonable prices for a foreseeable future, it could also become a lock-in instrument for ex ante investments in a commercial arrangement with a supplier whose broader geopolitical and economic interests may be incompatible with the peculiar interests of the consuming state or purchaser undertaking(s). This paper examines the key regulatory and policy issues relating to security of gas supply in the evolving EU energy market. It considers the recent ‘insecurities’ in the supply of gas from a legal and regulatory perspective.