How global oil flows would change if the United States blocks Iran's ports?

At 10:00 a.m. Monday (April 13) Eastern Time, the U.S. military began blocking ships from entering or leaving Iran’s ports. Reuters reported the move could prevent Iran from exporting about 2 million barrels of oil per day to global markets, tightening global oil supplies.

U.S. blockade and scope of the measure

The plan was announced after talks between the United States and Iran over the weekend in Islamabad, Pakistan ended without a deal. U.S. President Donald Trump said the Navy “will begin blocking any ships attempting to enter or leave the Strait of Hormuz.”

Later, CENTCOM clarified that the measure applies only to vessels bound for or departing Iran, including all of Iran’s ports in the Persian Gulf and the Gulf of Oman. CENTCOM also stressed that the U.S. will not impede freedom of navigation for vessels transiting the Hormuz Strait to reach or leave ports not controlled by Iran.

In response, Iran’s Islamic Revolutionary Guard Corps warned that any military vessel approaching the Strait of Hormuz would be deemed a ceasefire violation and would face a hard response. Iran’s armed forces, according to IRIB, said that if Iran’s ports and maritime transport hubs are threatened, security for all ports in the Persian Gulf and nearby areas, including the Gulf of Oman, would no longer be guaranteed.

Potential impact on oil exports and shipping

Analysts said obstructing Iran’s export activity would remove a significant supply from the global market. Commodity tracker Kpler data show Iran exported 1.84 million barrels per day in March and about 1.71 million barrels per day from the start of April to date. Those figures are higher than the 2025 average of 1.68 million barrels per day.

Kpler data also indicate that from the start of April to date, more than 180 million barrels of Iranian oil remained on offshore ships after Iran had ramped up production and shipments before the conflict escalated on February 28.

Even after Washington and Tehran reached a two-week ceasefire last week, shipping through the Hormuz Strait remained almost paralyzed. Since Iran blocked ships from passing Hormuz after hostilities began, shipping along the sea lane has been severely disrupted, with oil tankers continuing to avoid the area on Monday due to security concerns.

Ship movements and tanker inventories

Ship-tracking data showed that on Sunday, two Pakistan-flagged oil tankers—Shalamar and Khairpur—entered the Gulf to receive cargo from the United Arab Emirates (UAE) and Kuwait. On the same day, the very large crude carrier Mombasa B, flagged Liberia, transited the Hormuz Strait into the Gulf to receive cargo.

The day before, three fully laden supertankers left the Gulf through the Hormuz Strait—reported as the first ships to depart the area since the U.S. and Iran reached a ceasefire.

Kpler data show that as of last Tuesday, 187 fully laden oil tankers were in the Gulf region, carrying a total of 172 million barrels of crude oil and other refined fuels.

Where Iranian oil is headed

Before the conflict, most of Iran’s oil exports went to China, the world’s largest crude importer. However, last month the U.S. announced sanctions exemptions allowing other countries to import Iranian oil. Vessel-tracking data from London’s LSEG and Kpler indicate India is expected to receive Iran’s first crude cargo in seven years this week.

Before the conflict, about 20% of global oil and natural gas exports were transported through the Hormuz Strait, most heading to Asia, the world’s largest energy-importing region.

Market reaction

Even as the U.S. began implementing the blockade on ships tied to Iran, Trump’s Monday remarks that Iran “wants a deal” helped improve market sentiment. In the same day’s trading session, Brent settled at $99.36 per barrel and WTI settled at $99.08 per barrel. In early Asian trading on Tuesday (April 14), oil prices fell as investors priced in continued talks between the U.S. and Iran.