Maritime Boundary Delimitation
How international law draws lines in the ocean and resolves disputes over overlapping maritime claims.
Drawing Lines in the Sea
When two states' maritime zones overlap, international law requires delimitation: drawing a boundary that divides the area between them. UNCLOS provides that delimitation of the EEZ and continental shelf shall be effected 'by agreement on the basis of international law' to achieve 'an equitable solution.' For territorial seas, the default is the median line (equidistant from both coastlines) unless historic title or special circumstances require otherwise.
The ICJ and international tribunals have developed a three-step methodology. First, draw a provisional equidistance line. Second, consider whether 'relevant circumstances' require adjusting the line. Third, check whether the result is grossly disproportionate to the respective coastal lengths. Relevant circumstances include the configuration of coastlines, the presence of islands, access to natural resources, economic dependence, and historic fishing rights.
