Experts call the document signed by the five leaders "the constitution" of the Caspian Sea.
However, with offshore Caspian oil and gas production already nearly at 2 million barrels of oil equivalent per day, the impact from new fields - if and when disputes about their ownership are settled - might be limited.
"The vast capacities of the two countries in different fields can be complementary and should be used more and more in the interests of the two nations and the other nations of the region", said Iranian President Hassan Rouhani, on Sunday.
The status of the Caspian Sea remains a key topic for discussions at the Caspian states' summits.
Putin also praised this clause, saying it would help "ensure the peaceful status of the Caspian Sea".
According to Tengrinews.kz, in the Caspian sea, which representatives from five countries tried to separate since the collapse of the Soviet Union, inhabited by 80 percent of all sturgeon, but its main riches - oil and gas.
Iran, which ended up with the smallest share of the sea under the terms of the convention, is viewed as a potential loser in the deal.
The summit was also attended by Azerbaijani President Ilham Aliyev and Gurbanguly Berdymukhammedov of Turkmenistan.
But the body of water is salty because it was once part of a the Paratethys Sea before it became land locked after land drifts and a fall in sea level - however, the difference is more important than just for the sake of names.
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Who beat Melbourne? None other than the criminal city of Vienna , best known for opera and having honestly way too many museums. In total, 68 cities have seen their liveability ranking improve over the past year, while it has declined in nine cities.
One issue is whether the Caspian Sea should be considered a sea or a lake.
If it was termed a sea, it would be covered by the global maritime law, namely the United Nations Law of the Sea.
But if it is defined as a lake, then it would have to be divided between all five countries - and a formula about who gets what is not the easiest of equations to solve.
Neither the provisions of the 1982 UN Convention on the Law of the Sea nor the principles applied to neighbors on transboundary lakes are applicable to the Caspian Sea.
At stake are resources including trillions of dollars' worth of hydrocarbons in the seabed, which holds about 50 billion barrels of oil and almost 9 trillion cubic meters of natural gas in proven or probable reserves.
And while some countries have pressed ahead with large offshore projects such as the Kashagan oil field off Kazakhstan's coast, disagreement over the sea's legal status has prevented some other ideas from being implemented.
The agreement also offers hope for the Caspian's ecological diversity and its depleted stocks of the beluga sturgeon, whose eggs are prized globally as caviar.
Between 80 and 90 percent of the world's caviar is sourced from the Caspian, but the numbers have been falling over the past few decades.