WASHINGTON—Since late last year, US authorities have seized at least seven vessels linked to the Venezuelan oil trade. This campaign is part of a larger effort to undercut the so-called “shadow” or “dark” fleet—a network of aging tankers transporting illicit oil between Iran, Russia, China, and Venezuela. Increasingly, the tactics used to seize these vessels blur the lines between economic warfare and old-fashioned gunboat diplomacy.
Financial intelligence firm S&P Global estimates that one in five oil tankers worldwide are used to smuggle oil from sanctioned countries. Even before the Venezuelan oil blockade, the US Department of the Treasury’s Office of Foreign Assets Control (OFAC) sanctioned many shadow fleet vessels for their involvement in the illicit trade of Iranian or Russian oil. But never before have US authorities enforced sanctions so aggressively—chasing tankers across the high seas in the shadow of Russian submarines (even when they are not actually carrying any Venezuelan oil).
On January 9, Sean Parnell, the Pentagon’s chief spokesman, summed up the administration’s approach with a post on X. US forces, he wrote, would “hunt down and interdict ALL dark fleet vessels transporting Venezuelan oil at the time and place of our choosing.” This approach raises two important questions separate from the tactical challenge of stopping the vessels: First, what is the legal basis for the seizures? And second, what do you do with a tanker once you seize it? For the administration to succeed in its stated ambitions against the shadow fleet, it will need to arrive at suitable answers to these urgent questions.
What is the legal basis?
Although US authorities have purportedly filed warrants to seize dozens more tankers linked to the Venezuelan oil trade, only two warrants have been unsealed to date: authorizations for the seizure of the M/T Skipper (previously known as the Adisa) and the Bella I (now known as the Marinera), both of which were sanctioned for their involvement in supporting Hezbollah and the Quds Force, one of the branches of Iran’s Islamic Revolutionary Guard Corps. At least three other seized vessels—the M/T Sophia, the Olina (formerly the Minerva M), and the Sagitta—were sanctioned in January 2025 pursuant to US sanctions on Russia.
Sanctions alone do not authorize the seizure or confiscation of property. Although the US president has broad powers to “investigate, regulate, or prohibit” transactions under the International Emergency Economic Powers Act (IEEPA), the statutory foundation for most sanctions, the president cannot rely on IEEPA to confiscate property unless the United States is engaged in an armed conflict. In wartime, US authorities are permitted to confiscate foreign property used in attacks against the United States under IEEPA, and they can invoke the longstanding maritime practice of “prize law,” which recognizes the capture of civilian enemy vessels as a legitimate form of equitable relief during conflict.
But despite months of military buildup in the southern Caribbean, a blockade on Venezuelan oil, and the January 3 operation resulting in Venezuelan leader Nicolás Maduro’s capture, the United States does not appear to be relying on its wartime authorities in the warrants unsealed to date. Instead, US authorities have relied on civil forfeiture laws, which allow the government to bring an action directly against property suspected of being involved in certain “specified unlawful activities,” such as supporting terrorists or violating sanctions.
According to the unsealed and heavily redacted warrant applications in the M/T Skipper and Bella I cases, the United States relied on broad US laws prohibiting the support of terrorism when executing the seizures. These laws generally have an expansive extraterritorial application, unlike US sanctions, which require some conduct or activities with a US nexus. The US government may have a difficult challenge in establishing US sanctions violations given the shadow fleet’s avoidance of US jurisdiction, especially since they can navigate the globe without the involvement of any US persons, dollars, or insurance.
Forfeiture proceedings are not free of legal risk, however, as the government must still prove by a preponderance of the evidence that the property is subject to forfeiture. What’s more, claimants—including shipowners, ship charterers, the consignees of cargo, and victims of terrorism—may challenge the proceedings. Victims of terrorism with US court judgments may claim that the blocked property of designated terrorist organizations or state sponsors of terrorism held by the US government should be available to satisfy a valid judgment.
US President Donald Trump issued an executive order on January 9 prohibiting judicial proceedings against Venezuelan oil revenues held by US authorities. However, this protection would not necessarily extend to blocked vessels. If a forfeiture is overturned, subsequent buyers of the property could face financial losses and be exposed to sanctions risks.
The seizures also raise serious questions regarding international maritime law. Although international maritime law generally prohibits countries from boarding and seizing ships from other nations in times of peace, vessels lacking a flag state face some headwinds when claiming this protection. In the case of the Skipper, Guyana’s maritime authority indicated that the ship had been falsely flying Guyana’s flag ahead of its seizure by US authorities. This is likely why other shadow fleet vessels are quickly raising the Russian flag—changing ownership and rebranding under new shell companies mid-voyage and even hastily painting the Russian tricolor on hulls in the midst of a cross-Atlantic chase. Even so, US authorities have thus far been undeterred by this tactic.
US allies and partners are also stepping up maritime seizures. Last month, the French navy intercepted a tanker named the Grinch in the Mediterranean sea, taking the vessel’s Indian captain into custody. French President Emmanuel Macron indicated that the vessel was subject to international sanctions and suspected of flying a false flag. Separately, two crude carriers from the dark fleet were detained in Malaysia before being released. Last October, France seized another sanctioned tanker, the Boracay, off its west coast before releasing it a few days later.
What happens after the seizure?
Seizing shadow fleet vessels might just be the easy part. While US authorities scramble to sell seized oil, handling an oil tanker is a far more daunting task. There are lessons to be learned from the United States’ enthusiastic pursuit of Russian oligarchs’ yachts in 2022. US authorities incurred $32 million in costs associated with transporting, storing, and maintaining one state-of-the art yacht, a number that would be dwarfed by the costs associated with hanging on to a fleet of tankers.
