US Naval Blockade Hammers Iran Oil Exports, Forces Floating Storage

By Nerijus Adomaitis and Ahmad Ghaddar May 1, 2026

U.S. Marines from the 31st Marine Expeditionary Unit depart USS Tripoli (LHA 7) to board M/V Blue Star III, a commercial ship suspected of attempting to transit to Iran in violation of the U.S. blockade of Iranian ports, April 28, 2026. U.S. forces released the vessel after conducting a search and confirming the ship’s voyage would not include an Iranian port call. (U.S. Marine Corps photo)

A U.S. naval blockade of Iranian ports has shrunk Tehran's oil exports, stranding a growing stockpile of crude on tankers as Iranian storage sites run out of space, shipping data showed and analysts said.

With some vessels switching off tracking systems and U.S. forces turning back Iranian tankers, how much crude Iran is delivering to customers, particularly main customer China, is impossible to measure.

Just a handful of carriers carrying Iranian crude have left the Gulf of Oman between April 13-25, oil analytics firm Vortexa said. That's down over 80% from a comparable period in March, when Iran exported 23.4 million barrels, LSEG data shows.

Some of Tehran's vessels have been intercepted by the U.S. after leaving Iranian ports, along with sanctioned container ships and Iranian tankers in Asian waters.

"At this stage, we estimate that around 4 million barrels of Iranian crude has successfully moved out of the Gulf of Oman. We are not currently able to confirm whether any of those vessels have since been interdicted," it said in an email to Reuters.

The loss of Iranian supply adds to wider market tightness as the war has effectively closed the Strait of Hormuz, curtailing oil exports from Saudi Arabia, the UAE, Kuwait and Iraq and sending prices higher, something the U.S. has sought to avoid.

Last month, the U.S. granted Tehran an unexpected temporary sanctions waiver on energy exports to allow prices to cool.

Benchmark Brent crude oil futures LCOc1 have jumped by about $50 a barrel since the Iran war began on February 28, raising prices of gasoline, diesel and jet fuel.

The International Energy Agency has called it the world's largest oil output disruption.

NO TANKERS EXITED GULF SINCE BLOCKADE - KPLER

Analysts at Kpler said they had not observed any Iranian crude tankers exiting the Gulf of Oman since the blockade began. U.S. authorities said on Wednesday their blockade was denying Tehran of much-needed revenue from crude exports. "Right now there are 41 tankers with 69 million barrels of oil that Iranian regime can't sell," U.S. Central Command (CENTCOM) said on Wednesday.

Iran's currency, the rial, fell to a record low against the U.S. dollar on Wednesday, highlighting the financial difficulties that face the oil-reliant economy. Despite the pressure, Iran is still loading crude at its main export hub on Kharg Island, maritime intelligence firm TankerTrackers said.

Satellite imagery shows at least 10 tankers parked off Iran's Chah Bahar port on the Gulf of Oman, it added. Iran pumped about 3.24 million bpd of crude in February, around half for domestic refining.

Yet, the country may be forced to start cutting output within a week or two, said Kpler analyst Johannes Rauball, with storage scant. Onshore storage is about 60% full, Kpler said, with stocks above 50 million barrels, and capacity at 86 million barrels.

Capacity constraints could force Iran to curb production in mid-June, consultancy FGE NextantECA estimated on April 15.

(Reuters)