Event guide · Maritime chokepoint

Bosphorus & the Turkish Straits

Every other chokepoint is somewhere remote. This one runs down the middle of a city of roughly sixteen million people, under four road and rail crossings, at points barely half a mile wide — and it is the only way out of the Black Sea for a large share of the world's wheat, maize, sunflower oil and a meaningful slice of its crude. It is also governed by a 1936 treaty that says less about commerce than most commentary assumes.

What are the Turkish Straits?

Two waterways and a sea, treated as one system. The Bosphorus runs about 19 miles (31 km) from the Black Sea through Istanbul into the Sea of Marmara; the Dardanelles runs about 38 miles (61 km) from Marmara out to the Aegean and the Mediterranean. Both are Turkish territorial waters throughout — this is not an international channel in the way Hormuz or Malacca are, and that legal difference is the whole reason a dedicated treaty exists.

How narrow is the Bosphorus?

Around 700 metres — under half a mile — at its tightest, with a double bend that forces large vessels to make sharp course changes in a strong surface current running out of the Black Sea. Roughly 40,000 vessels transit each year, including tankers moving on the order of three million barrels a day of crude and products, threading past ferries carrying commuters across the same water. Turkey has run a traffic separation scheme since the 1990s and imposes one-way transits and suspensions for large vessels, tankers carrying hazardous cargo, fog and adverse currents. Multi-day queues at either end are therefore routine and mostly uninteresting; the tail risk is a collision or fire in a channel lined with a dense urban population.

What is the Montreux Convention?

The 1936 Convention Regarding the Regime of the Straits, signed at Montreux, returned control of the straits to Turkey and remains in force. The parts that matter:

• Merchant shipping has freedom of passage in peacetime. Commercial vessels of all flags may transit. Turkey regulates safety and navigation but does not license trade through the straits at will. This is the most commonly misread point — Montreux is overwhelmingly a warship treaty.
• Warships of non-Black-Sea states are tightly limited — caps on individual tonnage, aggregate tonnage present in the Black Sea, and a maximum stay of 21 days, with advance notification required. Aircraft carriers are effectively excluded. This is why outside naval power in the Black Sea is structurally limited regardless of anyone's intentions.
• In wartime, Turkey may close the straits to belligerents' warships, and has broader discretion if it is itself a belligerent or considers itself under imminent threat.

Turkey invoked the wartime provisions in late February 2022, closing the straits to the warships of belligerent states. The consequence was symmetrical and frequently misunderstood: it prevented Russian naval reinforcement from the Mediterranean into the Black Sea, and equally prevented Western warships from entering. It did not, and could not, stop grain or oil ships. Any Bosphorus scenario analysis that treats Montreux as a commercial lever starts from a false premise.

Why the exposed commodity is grain

The Black Sea basin is one of the world's great agricultural export regions. Russia is the largest wheat exporter in the world; Ukraine is a major exporter of wheat, maize, barley and by far the largest exporter of sunflower oil. Together they account for roughly a quarter of global wheat trade, and the overwhelming majority of it leaves by ship through the Turkish Straits. Fertiliser adds a second channel — Russia is a leading exporter of potash, urea and ammonia, though a substantial share of that moves through Baltic rather than Black Sea ports, so the exposures are related but not identical.

That mix makes a Bosphorus event a food-price event before it is a freight or energy event, and food prices transmit differently. They hit import-dependent emerging economies in North Africa and the Middle East directly, feed into headline inflation faster than most inputs, and carry political consequences that other commodity shocks do not.

What the 2022–23 grain corridor showed

The invasion of Ukraine in February 2022 halted Ukrainian seaborne exports almost entirely and wheat futures reached record highs in March. In July 2022 a UN- and Turkey-brokered arrangement — the Black Sea Grain Initiative — reopened three Ukrainian ports under an inspection regime coordinated from Istanbul, and moved tens of millions of tonnes over the following year. Russia withdrew from it in July 2023. Ukraine then established its own coastal corridor running close to Romanian and Bulgarian territorial waters, and export volumes substantially recovered without any agreement in place.

Three durable lessons sit in that sequence, and they generalise beyond grain. First, the initial price spike overshot the eventual physical shortfall by a wide margin — prices had largely retraced within a year. Second, the binding constraint was insurance and inspection, not the straits themselves; the water was never blocked. Third, alternative routing appeared faster than consensus expected, including rail and barge through the Danube and EU solidarity lanes, at higher cost and lower volume. Farlens scores this class of event on observable flow and insurance behaviour rather than on the announcement, because the announcement and the tonnage repeatedly diverged.

Which sectors feel a Bosphorus disruption — both sides

Sector patterns describe historical tendencies, not predictions or recommendations. Any given episode can and does break the pattern.

A short history of Turkish Straits disruptions

• 1915–16 (Gallipoli) — the Dardanelles campaign; the original demonstration that these straits are easier to defend than to force.
• 1936 — the Montreux Convention restores Turkish control and sets the warship regime still in force ninety years later.
• 1979 and 1994 — the Independenta and Nassia tanker casualties, both with heavy loss of life and both closing the strait for days. These accidents drove Turkey's traffic separation scheme and its restrictions on hazardous-cargo transits.
• February 2022 onward — Montreux wartime provisions invoked; Ukrainian seaborne exports collapse and wheat hits record highs.
• July 2022 – July 2023 — the Black Sea Grain Initiative operates and then lapses; a Ukrainian coastal corridor restores much of the volume without it.
• Late 2022 — tanker queues form at the straits over insurance verification following the G7 crude price cap: a paperwork constraint producing a physical backlog, which is the modern shape of a chokepoint problem.

Could the Bosphorus be bypassed?

Turkey has long promoted Kanal İstanbul, a proposed artificial waterway west of the Bosphorus intended to relieve traffic. Its status under Montreux is disputed — the treaty covers the straits, and a new canal outside them raises obvious questions about tolls and warship transit that no party has resolved. The project has been announced, costed and deferred more than once. Until something is actually dug, the practical position is unchanged: there is one way in and out of the Black Sea by sea, it passes through central Istanbul, and it is governed by a treaty that regulates navies rather than cargo.

Related reading

• Suez Canal — the everything-else chokepoint
• Strait of Malacca — the busiest chokepoint nobody talks about
• Strait of Hormuz — the oil chokepoint
• All Farlens event guides