On balance, their positive characteristics outweigh the negative ones, in particular because the market entry issue can be addressed by standardising long-term contracts and thus rendering them tradable. Similar considerations apply to the question of unbundling vertically integrated energy companies that operate the gas or electricity networks through which they transport their energy. From a pure security of supply point of view, rather than from a market efficiency point of view, some degree of vertical integration can provide stability and market power in negotiations with importers for domestic energy companies.