ORBIS

Chokepoint · Istanbul

Bosphorus

Disrupted since July 2026Updated October 1, 2026

The Bosphorus is the strait that runs through the middle of Istanbul, Turkey, between Europe and Asia. It joins the Black Sea to the Sea of Marmara and, through the Dardanelles, the Mediterranean. It is 31 km long and about 700 meters wide at its narrowest. It is the only sea route out of the Black Sea.

Ship counts from IMF PortWatch · Oil flows from the US Energy Information Administration

Istanbul and the Bosphorus seen from the International Space Station, with the Black Sea at the top Map showing where the Bosphorus is
Istanbul and the Bosphorus from the International Space Station, 2004. NASA, public domain.
Width at the narrowest
700 m
near Rumelihisarı
Length
31 km
through the middle of Istanbul
Ships in 2025
40,172
Turkey's count of all ships
Cargo ships a day
52
Last four weeks; 97 a day in 2023
Country
Turkey

Where is the Bosphorus?

The Bosphorus runs 31 km through Istanbul, with Europe on its western bank and Asia on its eastern bank. It joins the Black Sea in the north to the Sea of Marmara in the south. From the Sea of Marmara, ships reach the Mediterranean through a second strait, the Dardanelles. The narrowest point is about 700 meters, near the fortress of Rumelihisarı.

Map of the Bosphorus running through Istanbul from the Black Sea to the Sea of Marmara, with Europe to the west and Asia to the east EUROPE ASIA Black Sea Sea of Marmara Rumelihisarı Old city ISTANBUL 700 m
Map of the Bosphorus running through Istanbul from the Black Sea to the Sea of Marmara, with Europe to the west and Asia to the east EUROPE ASIA Black Sea Sea of Marmara Rumelihisarı Old city 700 m

Is the Bosphorus open?

Yes, to merchant ships, but traffic has fallen. Turkey has not closed the strait. Ukraine's sea drones first hit Russia's "shadow fleet" tankers on November 29, 2025. From July 2026 the attacks grew on both sides. Ukraine struck Russian ports and oil terminals. Russia attacked ports around Odesa 124 times in July, and cargo there fell by more than 90%.

On August 3, drones hit two Turkish-owned ships near Novorossiysk. No one claimed the attack. From August 6 to 9, Turkey held up ships bound for Novorossiysk and some Ukrainian ports, then let them pass. On September 16, the insurers' Joint War Committee listed the whole Black Sea as a war-risk area, which raises insurance costs for every ship. Most of the fall is grain. Ukraine's exports of farm goods fell from 2.6 million tonnes in August 2025 to 1.13 million in August 2026. In the four weeks to September 27, about 52 cargo ships a day passed through, against 97 in 2023.

Ships through the strait each day

Weekly average, January 2023 to September 2026

02550751001251502023202420252026Jul 2026Attacks on ships escalate 0255075100125150202420252026Jul 2026Attacks on ships escalate
2023 average, 97 a dayIMF PortWatch counts cargo ships and tankers from ship tracking data. Ships with their transponders off are not counted.

Who can sail through the Bosphorus?

Turkey controls the Bosphorus under the Montreux Convention of 1936. In peacetime, merchant ships of every country may pass freely. Warships of countries outside the Black Sea may usually have no more than 30,000 tons in the Black Sea at one time, and each may stay no more than 21 days. On February 28, 2022, four days after Russia invaded Ukraine, Turkey closed the straits to Russian and Ukrainian warships, except those returning to their home ports. It also asked other countries not to send warships.

Who may pass

  • Merchant shipsFree passage in peacetime
  • Warships from outside the Black SeaUsually at most 30,000 tons in the Black Sea at once, and 21 days each
  • Since February 28, 2022Closed to Russian and Ukrainian warships, except those returning to their home ports
Montreux Convention, 1936.

How much oil goes through the Bosphorus?

In the first half of 2025, about 3.7 million barrels a day passed through the Turkish Straits, about 60% of it crude oil. The US Energy Information Administration measures traffic at the Dardanelles. About 3.3 million of those barrels passed the Bosphorus. The rest was loaded at Turkish ports on the Sea of Marmara. There is no sea route around the strait, so every tanker leaving a Black Sea port must pass Istanbul. Kazakhstan was the largest exporter, shipping crude through the Caspian Pipeline Consortium's terminal near Novorossiysk. In April to June 2026, oil through the Turkish Straits rose to 4.1 million barrels a day.

Oil through each chokepoint

Early 2025Apr–Jun 2026
  1. Strait of Malacca16.6
  2. Cape of Good Hope9.4
  3. Bab el-Mandeb8.1
  4. Suez Canal5.8
  5. Strait of Hormuz4.9
  6. Danish straits4.7
  7. Turkish Straits4.1
  8. Panama Canal3.2
Million barrels a day, January to June 2025 and April to June 2026. US Energy Information Administration.

The strait over the years

  1. 1453Sultan Mehmed II takes Constantinople, a year after building the Rumelihisarı fortress at the narrows.
  2. 1915On March 18, mines sink Allied battleships trying to force the Dardanelles. The Gallipoli campaign costs about 250,000 Allied casualties.
  3. 1936The Montreux Convention, signed July 20, gives Turkey control of the straits.
  4. 1946The Soviet Union demands joint control of the straits, one of the pressures behind the Truman Doctrine.
  5. 2022Turkey closes the straits to Russian and Ukrainian warships on February 28, after Russia invades Ukraine.
  6. Sep 2026On September 16, insurers list the whole Black Sea as a war-risk area after attacks on dozens of merchant ships.

Other chokepoints

All 10 chokepoints →
Disrupted Suez Canal Traffic is recovering but still well below 2023. 40 ships a day, against 74 in 2023. Open Strait of Gibraltar Traffic close to normal. 133 ships a day, against 146 in 2023. Disrupted Strait of Hormuz Tankers cross under US protection; Iran still attacks ships. 4 ships a day, against 92 in 2023.
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