The Montreux Convention Regarding the Regime of the Straits

Montreux, Switzerland - 20 July 1936

The Montreux Convention is a multilateral treaty that governs the transit of vessels through the Bosphorus and Dardanelles Straits. It grants Turkey full control over the Straits but guarantees the free passage of civilian ships in peacetime.

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Key Provisions

The Convention balances Turkey’s security interests with the international community’s interest in freedom of navigation.

Merchant Vessels

• Peacetime: Merchant vessels enjoy complete freedom of passage and navigation in the Straits, by day and by night, under any flag with any kind of cargo, without any formalities.
• Wartime:
  • If Turkey is not a belligerent, merchant vessels under any flag or with any cargo enjoy freedom of transit.
  • If Turkey is a belligerent, merchant vessels not belonging to a country at war with Turkey shall enjoy freedom of transit on condition that they do not in any way assist the enemy.
  • Passage for merchant vessels of countries at war with Turkey is at the discretion of Turkey.

Warships

• Peacetime:

  • Black Sea Powers: Black Sea states (Turkey, Romania, Bulgaria, Georgia, Russia, and Ukraine) may send warships of any tonnage through the Straits, provided they pass singly and with prior notification to Turkey.
  • Non-Black Sea Powers: The aggregate tonnage of all foreign naval forces in transit through the Straits must not exceed 15,000 tons. The total tonnage that non-Black Sea powers can have in the Black Sea at any one time is limited to 45,000 tons, and no one country may have more than two-thirds of that tonnage. Vessels may remain in the Black Sea for a maximum of 21 days.
  • Aircraft Carriers: The Convention is widely interpreted as prohibiting the passage of aircraft carriers.

• Wartime:

  • If Turkey is not a belligerent, warships of belligerent powers are not permitted to pass through the Straits, except to return to their bases.
  • If Turkey is a belligerent, or considers itself to be under the imminent threat of war, the passage of warships is left entirely to the discretion of the Turkish government.

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The Montreux Convention has been a durable instrument of regional stability. Its provisions, particularly those allowing Turkey to close the Straits to warships in wartime, have been a critical factor in managing regional conflicts, most recently during the full-scale war in Ukraine.