A coastal country's full territorial sovereignty over the ocean — the same legal authority it has over land — extends just 12 nautical miles from its coastline, under the UN Convention on the Law of the Sea. But that's not where a country's meaningful economic control over the ocean actually ends. A separate, far larger zone extends 200 nautical miles from shore, where a country doesn't hold full sovereignty but does hold exclusive rights to the resources — the fish, the oil, the gas, the minerals — found in the water and seabed below.
Two very different zones, doing two very different jobs
Within the 12-nautical-mile territorial sea, a coastal state's authority is close to absolute, similar to its authority over land, though foreign ships retain a right of "innocent passage" through it. The Exclusive Economic Zone (EEZ), extending to 200 nautical miles, is a fundamentally different kind of zone — foreign ships and aircraft retain full freedom of navigation and overflight through it, exactly as they would in international waters, but the coastal state holds exclusive rights to explore, exploit, conserve, and manage all natural resources within it, living and non-living, in the water column and on or under the seabed. A foreign vessel can freely sail through another country's EEZ; it cannot legally fish there, or drill for oil there, without that country's permission.
Why the line becomes a genuine source of conflict
Two hundred nautical miles is a substantial distance — large enough that EEZs frequently overlap between neighbouring countries whose coasts sit less than 400 nautical miles apart, requiring negotiated boundary agreements or, in unresolved cases, becoming a genuine source of ongoing dispute. Small, remote islands can also dramatically expand a country's effective EEZ far beyond its mainland coastline, since even a tiny island generates its own 200-nautical-mile zone around it — which is part of why control over small, sometimes uninhabited islands and reefs, particularly in resource-rich or strategically significant regions, has become such a consistently contested issue in modern geopolitics, disproportionate to the islands' size or population.
What we're still unsure about
The formal rules governing territorial seas and EEZs under the UN Convention on the Law of the Sea are clearly codified and widely ratified, so the legal framework itself isn't in serious dispute among most of the world's states. What remains genuinely unresolved, and often actively contested, is how those rules apply to specific, disputed features — whether a given rock or reef legally counts as an "island" capable of generating its own EEZ, versus a lesser feature that generates only a smaller territorial sea or no maritime zone at all, is a distinction the treaty defines only loosely, and it's precisely this ambiguity that fuels several of the world's most persistent maritime boundary disputes today.
This sits inside Maritime Law & the Law of the Sea, one of seven topics in Geopolitics, one of five domains in Geography, one of seventeen subjects the app can quiz you on.