Iran is moving tens of millions of barrels of oil through covert offshore networks to bypass the new U.S. blockade on its ports, maritime intelligence firm Windward AI says.

The blockade, which took effect April 13, came amid a two-week ceasefire and failed peace talks between the U.S. and Iran, and as President Donald Trump insisted the waterway must remain open, through which roughly 20% of the world’s oil passes.

"Iranian oil distribution continues through indirect routing and offshore transfer networks," Windward told Fox News Digital.

"As of April 13, at least 11 tankers carrying approximately 20 million barrels of Iranian oil are positioned offshore Malaysia within a ship-to-ship transfer hub," the firm determined.

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"These vessels are likely awaiting counterpart vessels for offloading or preparing for onward movement."

Windward also clarified that the concentration highlights Iran’s "continued use of offshore storage and transfer mechanisms."

This allows Iranian oil flows to "persist outside direct transit through the Strait."

"Dark activity remains a central enabler of ongoing operations, supporting both post-transit port calls and broader evasion strategies," Windward added.

"At the same time, Iranian oil flows are increasingly routed through offshore hubs, reducing reliance on direct Hormuz transit."

U.S. forces began implementing the blockade at 10 a.m. ET April 13 after Trump vowed to block "any and all ships from trying to enter or leave" the strait, following weeks of pressure on Tehran.

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As previously reported by Fox News Digital, the U.S. military confirmed Wednesday it stopped nine oil tankers from attempting to breach the blockade.

"During the first 48 hours of the U.S. blockade on ships entering and exiting Iranian ports, no vessels have made it past U.S. forces," U.S. Central Command (CENTCOM) said.

"Additionally, nine vessels have complied with direction from U.S. forces to turn around and return toward an Iranian port or coastal area," CENTCOM wrote on X.

Fox News was also told all nine vessels were oil tankers. None of the vessels ordered to turn around needed to be boarded by U.S. forces, a senior U.S. defense official said.

On the first "full day" of the blockade, April 14, however, under active U.S. enforcement, Windward noted vessel behavior indicating "a fragmented and uneven response to the blockade."

"Initial movements show a combination of continued transit, route deviation and potential evasion," the firm said.

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"Sanctioned and falsely flagged vessels remain active, with some proceeding through the Strait while others delay, reverse course or adjust routing patterns.

"Iranian oil flows continue through indirect distribution networks, with significant volumes accumulating offshore rather than transiting directly through Hormuz."

CENTCOM said the blockade would apply only to maritime traffic entering and exiting Iranian ports.

It stressed that U.S. forces would not "impede freedom of navigation" for vessels transiting the strait to and from other destinations.

The blockade on the key trade route would be enforced "impartially" against any vessels entering or departing Iranian ports, including those in the Persian Gulf and the Gulf of Oman.

So far, sanctioned and falsely flagged vessels continue to operate under evolving enforcement conditions.

Rich Starry, a U.S.-sanctioned handy-size tanker signaling laden status, resumed outbound transit after previously turning around.

Windward said that its routing did not follow the Larak Island corridor and instead aligned with the alternative outbound path proposed by Iran.

At the same time, Murlikishan, a U.S.-sanctioned chemical tanker, was also observed journeying inbound, Windward clarified.