About 80 percent of global trade by volume moves by sea, according to the United Nations Conference on Trade and Development. Most of that traffic follows routes that look wide open on a map. In reality the busiest lanes squeeze through a handful of straits and canals, some only a couple of miles across. Close one for a week and prices change around the world. Close two and governments start counting reserves.

These chokepoints have always mattered to navies and shipowners. Recent years have made them matter to everyone else.

The Strait of Hormuz

Hormuz, between Iran and Oman, is the most important oil passage on earth. The US Energy Information Administration has estimated that around 20 million barrels a day of oil and petroleum products moved through it in recent years, about a fifth of global petroleum liquids consumption. A comparable share of the world's liquefied natural gas, mostly from Qatar, goes the same way.

The strait is about 21 miles wide at its narrowest point. The shipping lanes themselves are only two miles wide in each direction, separated by a buffer zone. There are limited alternatives. Saudi Arabia's East-West pipeline and a pipeline from the United Arab Emirates to the port of Fujairah can carry part of the volume around the strait, but not all of it.

The risk is not hypothetical. During the so-called Tanker War of the 1980s, during the Iran-Iraq conflict, hundreds of commercial vessels were attacked, and the United States escorted reflagged Kuwaiti tankers in a long naval operation. Since then, incidents including tanker seizures and mine attacks have kept the area a constant concern for insurers.

The Strait of Malacca

Between Malaysia, Indonesia and Singapore lies the Strait of Malacca, the shortest sea route between the Indian and Pacific Oceans. More than 80,000 vessels pass through it each year, carrying Middle Eastern oil to East Asia and Asian manufactured goods to Europe. The EIA has put oil flows there above 20 million barrels a day.

The channel narrows to under two miles near Singapore, and the water is shallow in places, which limits the size of ships. For China, which imports most of its oil by sea, the strait is a well-known vulnerability. In 2003 President Hu Jintao described it as a "dilemma," and Beijing has since invested in pipelines from Myanmar and Pakistan and in ports along the Indian Ocean as ways to reduce its dependence.

Piracy once plagued the strait. Coordinated patrols by Indonesia, Malaysia, Singapore and Thailand, begun in the mid-2000s, brought attacks down sharply.

Suez and the Red Sea

The Suez Canal carries roughly 12 percent of global trade and about 30 percent of container traffic, according to figures widely used by the shipping industry. It connects the Mediterranean to the Red Sea, which then narrows at the Bab el-Mandeb strait off Yemen.

The canal's vulnerability was demonstrated in March 2021, when the container ship Ever Given ran aground and blocked it for six days. Hundreds of ships waited. Estimates of the daily value of trade held up ran into the billions of dollars.

A far longer disruption began in late November 2023, when Houthi forces in Yemen began attacking commercial ships in the Red Sea, saying the strikes were linked to the war in Gaza. Many major carriers stopped using the route and sent their vessels around the southern tip of Africa instead. The Cape of Good Hope detour adds roughly 10 days or more to an Asia-to-Europe voyage, depending on the ports involved, and burns far more fuel. By early 2024, traffic through the Suez Canal had fallen to about half its normal level, and Egypt, which relies on canal fees for hard currency, reported a steep drop in revenue.

The US launched a naval coalition in December 2023, and the European Union followed with its own mission in February 2024. War-risk insurance premiums for Red Sea transits rose from a small fraction of one percent of a ship's value to as much as around 1 percent for some voyages, which on a large vessel means hundreds of thousands of dollars per passage. Conditions in the region have shifted since, and readers should check current shipping advisories rather than rely on any single snapshot.

The Panama Canal

Panama shows that chokepoints can fail for reasons that have nothing to do with war. The canal handles about 5 percent of global maritime trade, and it runs on fresh water. Each ship passing through the locks uses tens of millions of gallons drawn from Gatun Lake.

In 2023 a severe drought, tied in part to the El Niño climate pattern, lowered the lake. Authorities cut daily transits from roughly 36 to the low 20s and reduced the maximum draft allowed for ships. Vessels waited days, or paid steep fees for scarce slots. Restrictions were eased as rains returned, but the episode led to renewed talk of new water sources for the canal.

The Turkish Straits

The Bosporus and the Dardanelles link the Black Sea to the Mediterranean and are governed by the 1936 Montreux Convention. The treaty gives Turkey control over the straits and limits the passage of warships. After Russia's full-scale invasion of Ukraine in February 2022, Turkey invoked the convention to close the straits to the warships of countries at war. The same waterway later carried Ukrainian grain under a UN-brokered arrangement that operated from July 2022 until Russia withdrew in July 2023.

Who protects the lanes

The legal framework is the 1982 UN Convention on the Law of the Sea, which guarantees ships the right of transit passage through straits used for international navigation. The United States has never ratified the treaty but says it follows its navigation rules as customary law.

In practice, security depends on navies. The US Navy has long been the dominant guarantor, but others are increasingly present, including European, Indian, Chinese and Gulf forces. Coalitions are assembled ad hoc, and they are expensive. Escorting merchant ships is slow, and no navy has enough warships to cover every route at all times.

What shippers and governments do about it

• Reroute. Carriers can switch to longer paths, at the price of time and fuel.
• Hold more stock. Companies have moved away from strict just-in-time inventory for critical goods.
• Build bypasses. Pipelines, rail links and alternative ports reduce dependence, though never completely.
• Insure. War-risk cover is available but repriced after every incident.
• Diversify suppliers. Sourcing from several regions limits exposure to any single route.

None of these steps removes the underlying geography. Ships are large and cheap to operate per ton of cargo because they use direct routes. The same efficiency that keeps consumer prices low also means the system has little slack when a narrow passage closes, and a few miles of water remain among the most consequential real estate in the global economy.