Turkish Straits

What it is

The Turkish Straits are two narrow seaways in Turkey: the Bosphorus (Istanbul Strait, roughly 31 km long, minimum width about 700 m) and the Dardanelles (Canakkale Strait, roughly 61 km), separated by the Sea of Marmara. Together they form the only maritime corridor between the Black Sea and the Mediterranean, making them structurally indispensable to the seaborne trade of Russia, Ukraine, Bulgaria, Romania, and Georgia. The straits funnel roughly 3 million barrels of oil per day, mainly from Russia, Azerbaijan, and Kazakhstan. Turkey is the sovereign authority over both waterways and administers access under the 1936 Montreux Convention, which guarantees free passage for merchant ships in peacetime, restricts warship transit, and confers on Turkey the authority to close the straits to belligerent warships during conflict. Turkey collects transit fees from commercial vessels under the convention's cost-recovery mechanism.

History

The Bosphorus and Dardanelles were controlled by the Ottoman Empire for centuries and served as a strategic prize in the Crimean War (1853-1856) and the Gallipoli campaign of World War I (1915-1916). After the Ottoman defeat in World War I, the 1923 Treaty of Lausanne demilitarized the zone and placed it under an international commission. Turkey's request to refortify prompted the Montreux Conference in Switzerland; the resulting convention was signed July 20, 1936, and entered force November 9, 1936, with ten original parties: Australia, Bulgaria, France, Greece, Japan, Romania, Turkey, the USSR, the United Kingdom, and Yugoslavia. The convention restored Turkish military control while codifying commercial access rights, and it remains the governing instrument today. During World War II, Turkey invoked the convention's closure powers to deny passage to warships from both Axis and Allied sides, maintaining a costly neutrality. In February 2022, after Russia's full-scale invasion of Ukraine, Turkey invoked Article 19 of the convention to block warship transit by belligerent states, constraining Russia's Black Sea Fleet from reinforcement via the Mediterranean.

Current state

As of mid-2026, approximately 41,000 vessels transit the Bosphorus each year; combined traffic through both straits runs above 80,000 transits annually, making the corridor one of the busiest in the world by vessel count. Russia remains the largest single user by cargo volume. Turkey raised transit fees to US$6.70 per net tonne from July 1, 2026, a 15 percent increase under the convention's annual cost-recovery indexation, detailed in 土耳其将博斯普鲁斯海峡和达达尼尔海峡通行费上调15%，自7月1日起按净吨位收取6.70美元. Cumulative increases since 2020 have drawn objections from BIMCO and INTERCARGO, who argue the pace is pushing some bulk operators toward longer alternative routes. Turkey's proposed Canal Istanbul, a roughly 45 km artificial channel through Thrace parallel to the Bosphorus, has been in staged construction since 2021; if completed, it would provide an alternative route not subject to Montreux provisions, raising contested legal and strategic questions.

Relationships

Turkey holds sovereign authority and derives both revenue and diplomatic leverage from its gatekeeper position, a dynamic Ankara has deployed carefully throughout the Ukraine conflict and NATO negotiations. Russia's Black Sea Fleet and its commercial oil and grain exports depend structurally on Montreux passage rights, binding Moscow in its bilateral dealings with Ankara. Ukraine's grain exports route through the same corridor, making the convention's functioning a live economic variable in the ongoing conflict. NATO allies cannot freely rotate unrestricted warship tonnage into the Black Sea under Montreux tonnage limits, a constraint that became operationally significant in 2022. Bulgaria and Romania, as Black Sea NATO states, have a direct economic and security stake in the regime's stability.

What to watch

• Whether Canal Istanbul advances to a stage that forces a legal determination about Montreux applicability and triggers a renegotiation of the convention.
• Annual fee indexation trajectory and whether BIMCO and INTERCARGO succeed in prompting a formal convention review.
• Russia's diplomatic posture on the convention if warship restrictions or cumulative fees become economically unsustainable for Black Sea export economics.
• Ukrainian grain export volumes through the straits, a real-time indicator of how the convention functions under active wartime conditions.