On December 19, 2023, the U.S. Department of State announced the geographic coordinates defining the outer limits of the U.S. continental shelf in areas beyond 200 nautical miles from the coast. For convenience, the United States—and also this Essay—refers to the portion of a country's continental shelf that is beyond 200 nautical miles from the coast as the “extended continental shelf,” or ECS. The announcement states that the United States has ECS in seven different regions which collectively amounts to approximately a million square kilometers (about 380,000 square miles).

“Seldom has an apparent major change in international law been accomplished by peaceful means more rapidly and amidst more general acquiescence and approval,” Lauterpacht observed of continental shelf claims nearly seventy years ago. When considered today, this observation merits a caveat, as the question of how far the continental shelf extends into the sea is not yet fully settled. This article explores the customary international law applicable for determining continental shelf limits and also examines the legal procedures used by states to gain international acceptance of those limits.