Ashley Sherman, principal Caspian analyst at energy consultancy Wood Mackenzie, said that although the signing itself was "an unprecedented milestone" for the region, the immediate implications for the energy sector would be limited. Just $5 a month.
That is why disagreements over how to divide some of its huge oil and gas fields have been numerous - and acrimonious.
"Day of solidarity of Caspian Littoral States: Codifying cooperation on environment, shipping, fisheries, sustainable development & security w/o foreign military presence", Zarif said in a post on his official Twitter account on Sunday.
Global law provides formulas for dividing up the seabeds of lakes and seas.
The dispute began with the fall of the Soviet Union which had had a clearly defined Caspian border with Iran.
An Iranian woman rides a horse by the Caspian Sea coast in the port city of Gisum, in the northern province of Gilan in 2017.
Iranian President Hasan Rouhani, according to the news agency Interfax, says "this issue will be settled additionally in the course of agreements between the relevant parties".
The convention was signed by President Hassan Rouhani of the Islamic Republic of Iran, President Vladimir Putin of the Russian Federation, President Nursultan Nazarbayev of the Republic of Kazakhstan, President Ilham Aliyev of the Republic of Azerbaijan, and President Gurbanguly Berdimuhamedow of the Republic of Turkmenistan.More news: Subtropical storm Debby forms in the deep Atlantic
More news: Elon Musk says taking Tesla private is 'best path forward'
More news: Samsung Galaxy Watch vs Gear S3 in pictures
Crucially, the recent agreement may open the door to pipeline projects that have always been hostage to the ambiguity surrounding the Caspian's status.
Putin also outlined the prospects of cooperation between the Caspian states in the spheres of tourism, ecology and conservation of bio-resources, suppression of drug trafficking as well as prevention and liquidation of emergency situations, the Kremlin said. The convention reportedly stipulates that only countries through which a pipeline crosses would have to agree on the construction.
One of those is a pipeline across the Caspian which could ship natural gas from Turkmenistan to Azerbaijan and then further to Europe, allowing it to compete with Russian Federation in the Western markets.
But some are likely to view it as more of a breakthrough than others.
Even Russia at times argued it was a sea and not a lake. From there, the cargo is taken by rail to Afghanistan, where the United States has been militarily engaged since 2001.
Leaders of the five countries along its shores have signed a convention aimed at ending decades-long uncertainty over exploitation of its resources. The most hard hurdle was always going to be how to divide the sea's valuable resources, and that hurdle remains.
Details of the agreement have not been released.