For decades, debate in Iran over the Caspian Sea has often centered on a deceptively simple question: What percentage belongs to the country?
Iran, Russia, Azerbaijan, Kazakhstan and Turkmenistan all border the body of water. But the Caspian is treated neither as a conventional sea nor simply as an international lake.
Instead, the five countries have developed a special legal regime governing navigation, territorial waters, fishing, security and seabed resources.
The most important step came in 2018, when the five presidents signed the Convention on the Legal Status of the Caspian Sea in Aktau, Kazakhstan.
It established territorial waters of up to 15 nautical miles and an additional 10-nautical-mile exclusive fishing zone for each country. But it did not divide the entire Caspian into five fixed national shares.
Why doesn’t Iran own half the Caspian Sea
Before the Soviet Union collapsed in 1991, Iran and the Soviet Union were the only two countries bordering the Caspian.
The 1921 Russo-Persian Treaty of Friendship restored Iranian navigation rights restricted under Imperial Russia. A 1940 treaty further regulated trade and navigation.
None of the agreements, however, awarded Iran 50% of the Caspian.
Ahmad Vakhshiteh, director of the Moscow-based Center for Strategic Research on Developing Relations with the Middle East, says that this distinction is central to understanding the dispute.
“None of these treaties specified a percentage for either Iran or the Soviet Union,” he told DW. “They emphasized common use rather than dividing the sea into ownership shares.”
After the Soviet collapse, Azerbaijan, Kazakhstan and Turkmenistan emerged as independent states, turning a bilateral legal arrangement into a five-country negotiation.
Some Iranian politicians argued for a 50% share since it had previously shared the sea with the Soviet Union alone; others called for 20%. So far, neither claim has gained international recognition.
What the 2018 Caspian Sea agreement settled
“The Caspian is neither completely a sea nor completely a lake,” Vakhshiteh said.
“The 2018 convention created a special legal regime that distinguishes between the water, seabed, security and resources,” he added.
The convention does not divide the surface into national sectors. Each country has territorial waters and fishing zones, while other areas remain available for common navigation.
The seabed can be divided through agreements between neighboring states. These agreements matter because offshore oil and gas rights depend largely on such boundaries.
Russia, Kazakhstan and Azerbaijan have already reached several bilateral delimitation agreements. Iran’s southern boundaries remain among the more politically sensitive issues.
How security became central to Caspian Sea politics
The 2018 convention prohibits the presence of armed forces belonging to non-bordering states in the Caspian. Coastal countries are also not supposed to allow their territory to be used for military action against a neighboring Caspian state.
But Iran recently accused Ukraine of attacking an Iranian commercial vessel in the Caspian, killing a sailor. Kyiv said it had targeted vessels involved in transporting military cargo linked to Iran and Russia.
Vakhshiteh argues that such incidents demonstrate why Tehran considers keeping outside military powers away from the Caspian a strategic priority.
“Iran may still negotiate over seabed boundaries, but on one important principle a common legal rule already exists: the Caspian should not become a military base for powers from outside the region,” he said.
Currently, Iran is the only one of the five signatories that has not completed parliamentary ratification of the convention.
Oil and gas in the Caspian Sea
Behind the legal and military debates is another major issue: energy in the form of oil and gas.
Azerbaijan and Kazakhstan have developed substantial offshore oil resources, while Turkmenistan possesses major natural gas reserves.
Umud Shokri, an energy strategist and senior visiting fellow at George Mason University, says that Iran has meaningful hydrocarbon potential, too.
Its most important Caspian discovery, Sardar-e Jangal, was found in 2012 but development has been slow and it has not entered commercial production.
Iranian estimates suggest the area may contain around 2 billion barrels of oil, with roughly 500 million potentially recoverable, plus natural gas.
“Iran has confirmed hydrocarbon discoveries and promising prospects, but its commercially recoverable Caspian resource base remains uncertain and largely undeveloped,” Shokri told DW.
The southern Caspian is significantly deeper than many of the areas developed by Iran’s neighbors. Sardar-e Jangal lies in water around 700 meters deep, requiring advanced drilling equipment, subsea technology and substantial investment.
Sanctions have made access to international companies, financing and specialized offshore technology much harder. The country also has simpler options.
“Iran has huge oil and gas fields in the Persian Gulf and onshore that are generally easier and cheaper to develop,” Shokri said.
For Tehran, investing billions in difficult deepwater Caspian projects has often been less attractive than expanding production around the Persian Gulf like its South Pars gas field.
So, who owns the Caspian?
In the end, no single country owns or controls the Caspian Sea. And no treaty gives Iran, Russia or any other state a fixed share of the body of water.
The five neighboring states have territorial waters and exclusive fishing zones, while other parts remain open to common use.
Seabed boundaries, which determine many offshore oil and gas rights, are negotiated separately between neighboring countries. For Iran, that means some of its offshore resource rights are still subject to negotiation.
But ownership percentage is no longer the central question.
Today, the bigger issues are a combination of how the Caspian’s resources are managed, where maritime boundaries are drawn and its ability to keep out external military forces.
Edited by: Tim Rooks
