What does international law tell us about the US seizure of an oil tanker off the coast of Venezuela?

“We’ve just seized a tanker on the coast of Venezuela – a large tanker, very large, the largest one ever seized actually,” said Donald Trump on December 10. In a dramatic operation, US forces had just taken over an oil tanker called Skipper, which was sanctioned by the US in 2022 while sailing under a different name. “I assume we’re going to keep the oil,” the US president added later.

Venezuela has been under US-imposed sanctions since 2019, when Trump was first in the White House. And recent months have seen US forces target several vessels in the Caribbean, predominantly off the coasts of Venezuela and Colombia, each alleged to be trafficking drugs from the region. These strikes have killed more than 80 people so far.

The seizure of the Skipper marks the latest episode in the increasingly hostile relationship between Trump and Venezuela’s president, Nicolás Maduro. But what does international law have to say about the seizure?

Offering an official legal justification, US attorney-general Pam Bondi stated that US forces acted in execution of “a seizure warrant for a crude oil tanker used to transport sanctioned oil from Venezuela and Iran”. She added that the tanker had been sanctioned for many years “due to its involvement in an illicit oil shipping network supporting foreign terrorist organisations”.

The exact position of the seizure is not clear. Some accounts say it was seized “on the coast of Venezuela”, while others suggest the operation took place “in international waters”.

Assuming the seizure took place either in Venezuelan coastal waters or on the high seas, the international legal regime is governed by the 1982 UN Convention on the Law of the Sea (Unclos). The US is not a party to the convention, though it accepts the content as binding.

As a starting point, Unclos confers exclusive jurisdiction to the “flag state”. The Skipper appears to have been flying the flag of Guyana, which borders Venezuela, though Guyanese authorities were quick to attest that the ship was not registered there.

No other state is permitted to board or to enforce jurisdiction unless the seizure takes place in the seizing state’s coastal waters or the situation falls within a specific exception set out within Article 110 of the convention.

Such exceptions apply where there are reasonable grounds for suspecting that the ship is engaged in piracy, the slave trade or, in certain circumstances, unauthorised broadcasting. Exceptions also apply when the ship is without nationality or when the ship is, in reality, of the same nationality as the seizing warship.

Thus, it appears that Bondi’s claim that the Skipper was seized in accordance with domestically imposed sanctions has no standing in international law.

The International Tribunal on the Law of the Sea is also clear that states cannot unilaterally and arbitrarily board and enforce domestic law against foreign-flagged ships outside their own coastal waters unless Unclos provides an exception for doing so. Claims of suppressing criminality or terrorism would not, of themselves, suffice – certainly in relation to seizures on the high seas.

However, the fact that the ship’s registration in Guyana has come under question does open up a possible legal avenue for the seizure. This is because Unclos permits boarding in circumstances where a ship “is without nationality”.

In such circumstances, international law treats ships as “stateless vessels” and as outside the protection of any country. This is a claim that the US advanced in 1982 when seizing a stateless vessel off the eastern US coast controlled by suspected drug traffickers.

Researchers are divided, though, on whether there is a general right to retain the proceeds of such seizures under international law. And notwithstanding the doubts over the Skipper’s registration, this is not the legal approach that the US has sought to rely on.

A further, and perhaps more consequential, question remains: whether the seizure of the Skipper could be characterised as an act of war on the part of the US. International law is concerned with the objective existence of armed conflict rather than declarations of war and, in theory, an instance of “invasion or attack by the armed forces of a state on the territory of another state” would qualify. This could, potentially, include the seizure of another state’s vessel.

Relatively small-scale engagements, however, are not thought to qualify as “armed conflict”. For instance, France’s sinking of a UK-flagged ship called Rainbow Warrior in Auckland, New Zealand, in 1985 is not generally considered to have created a situation of “armed conflict”. Similarly, the Israeli raid on the Comoros-flagged Mavi Marmara in 2010 is not considered to have created a situation of armed conflict between those states.

Other approaches to establishing the existence of armed conflict look at levels of intensity or the organisation of any fighting between militaries. Though, at least for now, the threshold is unlikely to be met with regards to Venezuela and the US. The apparently stateless nature of the Skipper also creates a technical barrier to establishing a situation of “invasion” and, in turn, “armed conflict”.

One last question remains: whether Venezuelan officials were right to characterise the US military as “pirates, high seas criminals, [and] buccaneers”. It’s a tempting comparison to make, certainly, with the tendency to brand waterborne foes as “pirates”, an age-old rhetorical device that dates at least as far back as Roman orator Cicero, writing in the first century BC.

However, it is erroneous to apply the label to state or state-sponsored acts, with Article 101 of Unclos being clear that piracy can only be committed by private actors operating from private vessels. Whatever other legal issues the seizure might raise, being characterised as piracy is not one of them.

Mark Chadwick has previously received funding from the Arts & Humanities Research Council