For decades, the debate in Iran over the Caspian Sea, the world's largest lake, has often boiled down to a seemingly simple question: how much of it belongs to the country.
Five countries border the body of water - Iran, Russia, Azerbaijan, Kazakhstan and Turkmenistan. They have developed a special legal regime governing shipping, territorial waters, fishing, security and seabed resources.
The most important step was taken in 2018, when in Aktau, Kazakhstan, the five countries signed the Convention on the Legal Status of the Caspian Sea. It defined territorial waters up to 15 nautical miles wide and an additional exclusive fishing zone of 10 nautical miles wide for each country. But the treaty did not divide the entire Caspian Sea into five fixed national shares.
Why doesn't Iran own half of the Caspian Sea
Before the collapse of the Soviet Union in 1991, Iran and the USSR were the only two countries bordering the Caspian Sea. The 1921 Russo-Persian Treaty of Friendship restored Iranian navigation rights, which had been restricted under Tsarist Russia. A 1940 treaty further regulated trade and shipping. However, neither agreement grants Iran 50 percent of the Caspian Sea.
According to Ahmad Vakshiti, director of the Moscow-based Center for Strategic Studies for the Development of Relations with the Middle East, this distinction is key to understanding the dispute. "None of these treaties specify a specific percentage - neither for Iran nor for the Soviet Union. They emphasize joint use, not the division of the Caspian Sea into shares," the expert points out.
After the collapse of the Soviet Union, Azerbaijan, Kazakhstan and Turkmenistan became independent states, which turned the bilateral agreement into negotiations between five countries. Over the years, Iranian politicians have insisted on a 50 percent share, since the country previously shared the Caspian Sea only with the Soviet Union. Others have called for 20 percent, but so far none of these demands have received international recognition.
What the 2018 agreement stipulates
"The Caspian Sea is neither entirely a sea nor entirely a lake," says Ahmad Vakshite. "The 2018 Convention created a special legal regime that distinguishes between waters, seabed, security and resources," he explains.
The Convention does not divide the water area into national sectors. Each country has territorial waters and fishing zones, while the remaining areas remain accessible to general navigation.
The Caspian Sea bed can be divided through agreements between neighboring countries. These agreements are of great importance, since the rights to extract oil and gas depend largely on these borders.
Russia, Kazakhstan and Azerbaijan have already concluded several bilateral agreements. But the southern (Iranian) borders remain among the more politically sensitive issues.
How security became central
The 2018 convention prohibits the presence of armed forces belonging to states that do not border the Caspian Sea. Coastal states also have no right to allow their territory to be used for military action against a neighboring Caspian state.
But Iran recently accused Ukraine of attacking an Iranian merchant ship in the Caspian Sea, killing one sailor. Kiev, in turn, said it had struck ships involved in the transport of military cargo related to Russia and Iran.
According to expert Ahmad Vakshi, such incidents show why it is a strategic priority for Tehran to keep external military forces away from the Caspian Sea. "Iran may still be negotiating the borders, but there is already a consensus on one important issue - the Caspian Sea should not become a military base for countries outside the region," the expert says.
At the moment, Iran is the only one of the five parties to the convention that has signed but not yet ratified the document.
Oil and gas in the Caspian Sea
Behind the legal and military debate lies another important issue: oil and gas production. Azerbaijan and Kazakhstan are developing significant oil resources, while Turkmenistan has large reserves of natural gas.
According to energy expert Umud Shokri, Iran also has significant hydrocarbon potential. Its most important discovery in the Caspian Sea was made in 2012 - the Sardar-e Jangal field. But its development is progressing slowly and has not yet entered commercial exploitation.
According to Iranian estimates, it could contain about 2 billion barrels of oil, of which approximately 500 million can be extracted. There are also natural gas deposits there.
"Iran has confirmed hydrocarbon deposits, but its resource base in the Caspian Sea remains unclear and largely undeveloped," Shokri told DW.
The southern part of the Caspian Sea is significantly deeper than many of the areas being developed by Iran's neighbors. For example, the Sardar-e Jangal field is located at a depth of about 700 meters, which requires modern drilling equipment, subsea technology and significant investment. But sanctions have made it difficult for Iran to access international companies, financing and specialized offshore technology. But the country also has easier options.
"Iran has vast oil and gas fields in the Persian Gulf and onshore, which are generally easier and cheaper to develop," says Omoud Shokri. From this perspective, it is not particularly attractive for Tehran to invest billions in complex deep-sea projects in the Caspian Sea.
And yet: whose Caspian Sea is it?
Ultimately, no country owns or controls the Caspian Sea. And no treaty grants Iran, Russia, or any other country a fixed share of the Caspian Sea's waters.
The five neighboring countries have territorial waters and exclusive fishing zones, while the rest remains open to common use.
The seabed boundaries, which define many of the rights to oil and gas fields, are negotiated separately between the neighboring countries. For Iran, this means that some of its rights to the resources of the Caspian Sea are still up for negotiation. And how much of it the country owns is no longer the main issue. Today, it is much more important how the resources of the Caspian Sea are managed, where the borders are drawn, and how to keep foreign military forces out of the Caspian Sea.
Author: Amir Soltanzadeh