Turkish Straits shipping: oil, grain and the Montreux regime

Turkish Straits shipping moves roughly 3.7 million barrels of oil per day plus the bulk of Black Sea grain through two narrow channels that run past a city of 16 million people. The system comprises the Bosporus, the Sea of Marmara and the Dardanelles, and it is the only maritime exit from the Black Sea. Russia, Ukraine, Kazakhstan, Romania, Bulgaria and Georgia have no alternative sea route to world markets.

Its importance is not a matter of volume alone. The Strait of Malacca carries six times more oil, but Malacca has the Lombok and Sunda detours. Black Sea cargo has no equivalent. It transits the Turkish Straits or it does not leave by sea at all, which makes this the chokepoint where the gap between traffic and substitutability is widest.

Two forces govern it. One is legal: the 1936 Montreux Convention, which guarantees merchant passage in peacetime and gives Turkey discretion over warships. The other is physical: a channel narrowing to about 700 metres, with reversing currents and blind turns, that Turkish authorities may close on safety grounds at any time.

Key numbers

What flows through the Turkish Straits

Four cargo classes dominate. Crude oil and condensate account for 2.2 mb/d southbound through the Dardanelles, most of it Russian Urals loading at Novorossiysk and Kazakh CPC Blend loading at the adjacent Yuzhnaya Ozereyevka terminal. Refined products add another 1.5 mb/d. Together they place the straits fifth among the world's oil chokepoints, behind Malacca, Hormuz, Suez and the Danish Straits.

Grain is the second flow, and the one with the largest humanitarian footprint. Ukraine's maritime corridor, opened in August 2023 after Russia exited the Black Sea Grain Initiative, had carried 106.4 million tonnes of grain within 177.7 million tonnes of total cargo by March 2026. Every one of those cargoes exited through the Bosporus. Russian wheat, the largest single export flow in the global wheat trade, uses the same door.

LNG is small but structurally interesting: 0.6 bcf/d moves through the Dardanelles, mostly northbound, since Turkey and Black Sea states import gas that Russia once supplied by pipeline. The straits are one of the few chokepoints where energy flows run in both directions.

The fourth flow is naval. Under Montreux, Turkey has restricted warship transit since March 2022, when it recognised the Russia-Ukraine conflict as a war. That decision froze the naval balance inside the Black Sea, since neither belligerent can reinforce its fleet from outside.

Who depends on the Turkish Straits

Kazakhstan is the most exposed country in the system. The Caspian Pipeline Consortium carries roughly 80% of Kazakh oil exports to Novorossiysk, from where every barrel transits the Bosporus. A landlocked producer with no coastline on open water depends entirely on a channel it does not control, in a country it does not border. See CPC pipeline for the terminal-level detail.

Russia's dependence is partial but material. Novorossiysk loaded more than 980 kb/d of crude in June 2026, on the order of a quarter of the country's seaborne crude, all of it straits-bound. The Baltic and Pacific routes carry the rest, which gives Russia a flexibility Kazakhstan lacks. The full breakdown sits in Russian seaborne crude exports.

Ukraine's dependence is close to total for agricultural exports. Land routes through the EU proved politically fragile, most visibly when Polish hauliers blocked crossings in 2023 and 2024, and the Danube corridor carries a fraction of seaborne volume.

On the import side, Turkey, Bulgaria, Romania and Georgia depend on the straits for refined products and LNG. Egypt, Jordan, Pakistan, Bangladesh and much of North Africa depend on them indirectly, as buyers of Black Sea wheat.

Alternatives and bypass routes

This is where the straits differ from other chokepoints. The alternatives exist, but they are small relative to the flow.

The Baku-Tbilisi-Ceyhan pipeline is the only working bypass at scale, moving Azeri crude, Shah Deniz condensate and some Kazakh Tengiz barrels to the Mediterranean at Ceyhan. Capacity is 1.2 mb/d with drag-reducing agents. It bypasses the Black Sea entirely rather than relieving it, and its capacity is committed to Caspian production that would not otherwise transit the straits.

The Samsun-Ceyhan pipeline was the purpose-built answer, designed for up to 1.5 mb/d from the Turkish Black Sea coast to the Mediterranean. It was proposed in the 2000s, promoted by successive Turkish governments as the way to take tankers out of the Bosporus, and never built. The economics never closed without committed Russian and Kazakh volumes, and those producers preferred the cheaper sea route.

Kanal Istanbul, the artificial waterway Turkey has proposed alongside the Bosporus, remains a project rather than infrastructure. It also raises an unresolved legal question, since a canal outside Montreux's geographic scope could allow Turkey to charge transit fees and set its own rules, which is precisely why 104 retired Turkish admirals publicly objected in 2021.

For grain, the Danube river ports and EU land corridors are the practical alternatives. Both function, and neither matches seaborne capacity or cost.

The result: no combination of existing alternatives absorbs the 3.7 mb/d that crosses the Dardanelles, and no new capacity is under construction. A sustained closure is not a rerouting problem, it is a shut-in problem.

Historical incidents

Assets and companies exposed

Exposure concentrates in four groups. Tanker owners calling at Black Sea ports carry the most direct risk, and the July 2026 attacks hit Greek-controlled suezmaxes and Turkish-owned tonnage alike. Marine insurers and the Lloyd's war risk market price that exposure continuously; the move above 1% of hull value in July 2026 reprices every voyage in the basin.

Producers with straits-only export routes form the second group, most notably the CPC shareholder set and Kazakh upstream operators, whose barrels have no alternative outlet at scale. Third, Black Sea grain traders and the importing countries that buy from them. Fourth, Turkish coastal infrastructure and the Istanbul urban area itself, which bears the environmental consequence of any incident in the channel, as 1979 and 1994 demonstrated.

This page describes exposure. It does not assess securities or recommend positions.

What to watch

Novorossiysk and CPC loading volumes, tracked by Kpler and Vortexa and reported by Bloomberg, show whether Black Sea barrels are reaching the straits at all. Black Sea war risk premiums, quoted weekly in the London marine market, price the campaign in real time and pass through to freight. Turkish transit suspensions and TSVTS traffic notices reveal when Ankara is applying safety discretion, which in practice matters more than the legal text. Wheat benchmarks in Chicago and Euronext respond to corridor interruptions within days. Finally, any movement on Kanal Istanbul procurement would signal that Turkey is again pursuing a route outside the Montreux regime.

FAQ

How much oil passes through the Turkish Straits? About 3.7 million barrels per day of crude oil, condensate and refined products transited the Dardanelles in the first half of 2025, according to the EIA using Vortexa tanker tracking. That is close to 5% of world maritime oil trade, making the Turkish Straits the fifth largest oil chokepoint after Malacca, Hormuz, Suez and the Danish Straits.

Can ships avoid the Turkish Straits? Not for Black Sea cargo. The straits are the only maritime exit from the Black Sea, so any alternative means leaving by pipeline or by land. The Baku-Tbilisi-Ceyhan pipeline moves 1.2 mb/d of Caspian crude to the Mediterranean but bypasses the Black Sea rather than relieving it, and the purpose-built Samsun-Ceyhan bypass was never constructed.

What is the Montreux Convention? A 1936 treaty that governs passage through the Bosporus and Dardanelles. It guarantees merchant vessels freedom of passage in peacetime and gives Turkey discretion to restrict warships during war or perceived threat. Turkey invoked it on March 1, 2022, closing the straits to warships of Russia and Ukraine.

Why are the Turkish Straits considered dangerous to navigate? The Bosporus narrows to roughly 700 metres, bends sharply, and carries strong reversing currents, all within a densely populated city. About 50,000 vessels transit each year. The 1979 Independenta and 1994 Nassia collisions each killed dozens and closed the waterway, and both produced the traffic rules in force today.

How does Black Sea grain reach world markets? Almost entirely through the Turkish Straits. Ukraine's maritime corridor, opened in August 2023, had moved 106.4 million tonnes of grain by March 2026, all of it exiting through the Bosporus, alongside Russian wheat shipped from Novorossiysk and other Black Sea ports.

Has the Turkish Straits ever been closed to merchant shipping? Yes, though never for long. The Bosporus was closed for weeks after the Independenta fire in 1979 and suspended for days after the Nassia collision in 1994. Modern interruptions are typically hours-long safety suspensions ordered by Turkish traffic authorities rather than closures of the legal regime, which has held continuously since 1936.