Definitions also change from country to country. A country with limited access to cross-border energy infrastructures but a broad domestic resource base will thus think differently about the security of its energy supplies than a small, open economy closely interconnected with its neighbours but with few resources of its own. Not unlike the notion of “sustainability”, another key dimension of energy policy in OECD countries, the notion of security of energy supply is often being applied in different ways to support different policy objectives.