The North Sea is important within the European energy sector. In addition to the oil and gas reservoirs present beneath the seabed, the North Sea has been identified as a primary location to construct renewable energy infrastructure and may provide eight percent of the energy supply in Europe by 2030. Offshore oil and gas, offshore wind and ocean energy projects are capital intensive; billions of euros are required for the construction of many individual projects. It is common business practice to raise debt, which is more expensive when risks are greater. Security rights such as mortgage and pledge reduce the risks of lenders. It is currently impossible to mortgage installations situated on the seabed further than 22.2 kilometres off the Dutch coast. Allowing for such mortgages could benefit the development of the offshore energy sector as this would reduce risks. This contribution reviews an alternative which would allow for installations on this part of the seabed to be mortgaged. In this context law of the sea, the lex rei sitae, ownership of the seabed and rules of Dutch property law are discussed.