Explainer: What does the U.S. naval blockade of Iran mean for oil flows?

Explainer: What does the U.S. naval blockade of Iran mean for oil flows?
A billboard with a graphic design about the Strait of Hormuz on a building in Tehran, Iran, 13 April, 2026. Majid Asgaripour/WANA (West Asia News Agency)
Reuters

Since Monday, Monday (13 April), America has blocked traffic entering and leaving Iran's ports, in an escalation of the conflict in the Middle East. The consequences of that will continue to impact the global oil supply.

The U.S. Central Command said on Monday that unauthorised vessels entering or leaving ports that were blockaded faced "interception, diversion, and capture". 

Iran says this is an "act of piracy".

Central Command said that U.S. forces would not impede freedom of navigation for vessels transiting the Strait of Hormuz to and from non-Iranian ports.

This comes after a failure to agree on a peace deal at talks in Islamabad, Pakistan over the weekend. Since then, however, U.S. President Donald Trump announced a two-week ceasefire, which Israel has agreed to.

Iran's Revolutionary Guards have responded to this development, warning that military vessels approaching the strait would be considered a ceasefire breach and dealt with harshly and decisively.

Oil supplies around the world

The blockade would prevent roughly two million barrels of Iranian oil a day from entering the world's markets, further tightening global supply.

March saw Iran export 1.84 million barrels of crude oil per day compared to 1.71 million per day so far in April totalling 180 million barrels in the first week of this month.

Most of that, around 100 million barrels, is being stored out at sea and floating in waters off Malaysia and Indonesia, and China.

Ships hesitant to move through Strait

Hours before the U.S. blockade was imposed on Monday, two Pakistan-flagged tankers, Shalamar and Khairpur, entered the Gulf to load cargoes from the United Arab Emirates and Kuwait. A Liberia-flagged very large crude carrier (VLCC) Mombasa B, became the third ship that transited the strait on Sunday and was ballasting in the Gulf.

A Malta-flagged ship destined for Vietnam tried to pass through the strait on Sunday but turned back and anchored near the Gulf of Iran. It was due to load Iraq crude oil to take to Asia.

The Malta-flagged VLCC Agios Fanourios I, which tried to pass through the strait on Sunday to load Iraqi crude destined for Vietnam, turned back and was anchored near the Gulf of Oman.

Reports by Kpler, which provides intelligence tools for trade, say 187 laden tankers carrying 172 million barrels of crude oil and refined products were inside the Gulf in the first seven days of April.

Iran has warned that they will hit Gulf ports if the U.S. carries out its blockade.

Before the war, 20% of the global oil and natural gas flowed through the Strait of Hormuz.

Impact of sanctions

At the beginning of February, America's State Department announced what they called "Sanctions to Combat Illicit Traders of Iranian Oil and the Shadow Fleet". This officially restricted "15 entities, two individuals, and 14 shadow fleet vessels connected to the illicit trade in Iranian petroleum, petroleum products, and petrochemical products".

The U.S. said the move was to pressure the Iranian regime to act against illegal trade of oil claiming Iran is using the revenues for "oppressive behavior and support terrorist activities and proxies".

These sanctions are now seen as the precursor to the dramatic and sudden escalation in the conflict later that month.

China was the biggest recepient of Iranian crude oil before the Middle East conflict but a U.S. sanctions waiver has widened the Iranian oil market to countries such as India, the most populated nation in Asia. Two shipments have arrived into Indian ports this week, according to shipping data from LSEG.

Read more of our coverage about the worldwide impact of restricting shipping in the Gulf:

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