Caspian Sea Ownership Remains Unresolved Despite 2018 Convention

Five countries touch the Caspian Sea, but none of them owns it. This simple fact has shaped decades of negotiation, dispute, and compromise among Iran, Russia, Azerbaijan, Kazakhstan, and Turkmenistan—a tangle of competing claims that culminated in 2018 with a convention that solved some problems while leaving others deliberately unresolved.

For much of the twentieth century, the question seemed straightforward. Before the Soviet Union collapsed in 1991, only two nations bordered the Caspian: Iran and the USSR. They signed treaties in 1921 and 1940 that restored Iranian navigation rights and regulated trade, but neither document awarded either country a fixed percentage of the sea. The emphasis was on shared use, not divided ownership. When the Soviet Union fell apart, that bilateral arrangement shattered. Suddenly Azerbaijan, Kazakhstan, and Turkmenistan emerged as independent states, each with its own coastline and its own claims. Iranian politicians began arguing that since their country had once shared the Caspian with a single superpower, it deserved half. Others proposed 20 percent. Neither claim found international backing, and the question of ownership percentages has never been resolved.

The 2018 Convention on the Legal Status of the Caspian Sea, signed in Aktau, Kazakhstan, took a different approach. Rather than dividing the sea into five national slices, the five presidents created what amounts to a hybrid legal regime—neither fully a sea nor fully a lake. Each country received territorial waters extending 15 nautical miles from its coast, plus an additional 10-nautical-mile exclusive fishing zone. Beyond those boundaries, the water remains open to common navigation. The seabed, however, is negotiable. Neighboring countries can carve out bilateral agreements to determine who controls which underwater territory, a distinction that matters enormously because offshore oil and gas rights depend on those boundaries. Russia, Kazakhstan, and Azerbaijan have already reached several such agreements. Iran's southern boundaries remain among the most politically sensitive and, so far, largely unresolved.

The convention also addressed security in ways that reflect regional anxieties. It prohibits armed forces from non-bordering states from operating in the Caspian and bars coastal countries from allowing their territory to be used for military action against a neighboring Caspian state. This prohibition carries real weight for Iran, which views the Caspian as a strategic space that must remain insulated from outside powers. That concern became concrete when Iran accused Ukraine of attacking an Iranian commercial vessel in the Caspian, killing a sailor. Kyiv claimed the vessel was transporting military cargo linked to Iran and Russia. The incident underscored why Tehran considers the security clause central to its interests—a principle on which a common legal rule already exists, even as other disputes simmer.

Beneath the legal and military questions lies energy. Azerbaijan and Kazakhstan have developed substantial offshore oil fields. Turkmenistan holds major natural gas reserves. Iran, too, has hydrocarbon potential. Its most significant Caspian discovery, Sardar-e Jangal, was found in 2012 and may contain around 2 billion barrels of oil, with roughly 500 million potentially recoverable, plus natural gas. But development has stalled. The field lies in water approximately 700 meters deep, requiring advanced drilling equipment, subsea technology, and billions in investment. International sanctions have made it harder to access foreign companies, financing, and specialized offshore technology. For Iran, the calculation has often been straightforward: developing easier, cheaper oil and gas fields in the Persian Gulf and onshore makes more economic sense than pouring resources into difficult deepwater Caspian projects.

So who owns the Caspian Sea? The answer, after decades of negotiation, is no one and everyone. No single country controls it. No treaty grants Iran, Russia, or any other state a fixed ownership share. The five neighbors have their territorial waters and fishing zones. Other parts remain open to common use. Seabed boundaries are negotiated separately, case by case, between adjacent states. For Iran, this means some of its offshore resource rights remain subject to negotiation—a position that reflects both the sea's unique legal status and the unfinished business of regional politics. The central question has shifted from ownership percentages to something more complex: how the Caspian's resources are managed, where maritime boundaries are drawn, and whether it can remain a space insulated from external military powers. Those questions will shape the region's future far more than any claim to a percentage ever could.