Caspian Sea Convention

The Convention on the Legal Status of the Caspian Sea was signed on 12 August 2018 in Aktau, Kazakhstan, by the presidents of Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. It ended more than two decades of negotiations over how to classify the Caspian — historically disputed as either a sea (which would trigger the UN Convention on the Law of the Sea) or a lake (which would require equal division among littorals).

The Convention adopts a hybrid regime that treats the Caspian as neither fully sea nor fully lake. Key provisions include:

• A 15-nautical-mile territorial waters zone for each state, plus an additional 10-nautical-mile exclusive fishing zone.
• The water surface beyond national zones is designated for common use.
• The seabed and subsoil are to be divided into sectors by bilateral agreements between neighboring states — leaving some delimitation questions (notably between Iran, Azerbaijan, and Turkmenistan) unresolved.
• A prohibition on the military presence of non-littoral states in the Caspian, a long-standing Russian and Iranian priority.
• Provisions allowing submarine pipelines subject to environmental approval by states whose seabed sectors they cross — a clause with implications for any future Trans-Caspian Gas Pipeline between Turkmenistan and Azerbaijan.

The Convention entered into force after ratification by four of the five signatories. Iran has not ratified the treaty as of its signing through subsequent years, citing concerns over its seabed share, which under the framework is widely seen as smaller than the roughly 20% Tehran had historically claimed.

The agreement is significant for regional energy geopolitics, freedom of navigation, and the exclusion of outside military powers (such as NATO) from the basin. It is often cited as an example of a sui generis maritime regime tailored to a specific enclosed body of water.