Windward Finds Nearly 40% of Iran-Linked Tankers Using False Flags

Some +200 Iran-trading ships were either using fraudulent registries to flag vessels or falsely signaling they flew the flag of a country, based on designations provided by the International Maritime Organisation (IMO), the United Nations agency responsible for overseeing maritime regulation.

Windward examined the flag status of +540 tankers and gas carriers identified by the New York-based non-governmental organization United Against Nuclear Iran (UANI) as being involved in transporting crude, fuel oil, refined products, and liquefied propane and butane for Iran.

To understand the scale of deception, according to their IMO numbers, 40% of these tankers were falsely flagged — meaning they either used a fraudulent flag registry or falsely claimed to be registered under a legitimate one.

Of the +540 ships identified by UANI, +300 had been sanctioned by Western governments — including the US, UK, and EU — and most were flagged by Windward as high-risk vessels engaged in deceptive, evasive, or illicit practices.

The findings illustrate that Iran’s seaborne energy commodities trade is increasingly reliant on an illicit fleet of lawless tankers that deliberately operate outside the global rules-based order — a framework essential for keeping vessels seaworthy and safe, and for protecting the environment, oceans, and coastal states from pollution and oil spills.

Record numbers of falsely flagged tankers are shipping oil through vital maritime chokepoints, after sanctions imposed by Western governments on the so-called ‘dark fleet’ of Iran, Russia and Venezuelan-trading ships increased dramatically over the past nine months.

The result is a growing blind spot in maritime oversight — one that jeopardizes not only compliance but safety.

Vessels sailing under a ‘false flag’ lose the validity of any insurance or certification that verifies compliance with international maritime standards — compounding both safety and environmental concerns. The average age of ships in the UANI fleet is 22 years, already beyond the conventional 20-year operational lifespan. This dangerous mix of aging vessels and fraudulent credentials sharply increases the risk of accidents at sea.

Many legitimate flag registries are purging ships as they are sanctioned, with anonymous owners then flocking to sham registries.

Registries identified by the IMO as fraudulent and used by the UANI fleet include those purporting to represent Aruba, Benin, Curacao, Eswatini, Guinea, Guyana, and Sint Maarten.

Some +100 tankers in the UANI list were flagged with these countries, including 48 for Guyana, 16 with Guinea, and 16 with Curacao. These vessels represent a recurring pattern of abuse tied to specific jurisdictions.

The remaining vessels were falsely broadcasting they were flying the flag of a legitimate registry that IMO records showed they were not registered.

Thirty-three Iran-trading ships – all falsely flagged – were subject to Russia-related sanctions as they were previously involved in these trades, underscoring the nexus between the two countries.

China is the foremost destination for Iranian crude, which comprises about 15% of the country’s average 11.1m barrels per day of imports. This dependency fuels the logistical complexity behind Iran’s crude exports.

Many of the falsely flagged tankers are deployed solely within international waters to minimise regulatory reach but some are tracked within Chinese zones for extended periods without penalty.

The falsely flagged, sanctions-evading ships play a crucial role in an increasingly complex logistics chain that relies on as many as four or five tankers over one voyage to deliver a cargo of oil from Iran to a port in China.

They are used for ship-to-ship transfers and frequently found at anchor within international waters to store and then transfer Iranian crude to other vessels to obfuscate the cargo’s origin and destination.

As many as 30 falsely flagged tankers are currently tracked off Malaysia’s Riau archipelago, Windward data show. 

Based on Windward assessments, all participate in high-risk activities, including changing flags multiple times (a practice known as flag-hopping), identity tampering, conducting GNSS manipulation to ‘spoof’ their location or undertake dark activity for extended periods while undergoing subterfuge, unauthorised ship-to-ship transfers.