The natural prolongation principle or principle of natural prolongation is a legal concept introduced in maritime claims submitted to the United Nations.
The phrase denotes a concept of political geography and international law — that a nation's maritime boundaries should reflect the 'natural prolongation' of where its land territory reaches the coast. Oceanographic descriptions of the land mass under coastal waters became conflated and confused with criteria which are deemed relevant in border delimitation. This concept was developed in the process of settling disputes where the borders of adjacent nations were located on a contiguous continental shelf.
An unresolved issue is whether a natural prolongation defined scientifically without reference to equitable principles shall be construed as a "natural prolongation" for the purpose of maritime border delimitation or maritime boundary disputes.
History
The phrase natural prolongation was established as a concept in the North Sea Continental Cases in 1969.
The relevance and importance of natural prolongation as a factor in delimitation disputes and agreements has declined during the period in which international acceptance of UNCLOS III has expanded.
The Malta/Libya Case in 1985 is marked as the eventual demise of the natural prolongation principle being used in delimiting between adjoining national maritime boundaries.