Tensions between the US and Venezuela are soaring after American forces seized an oil tanker in the Caribbean Sea.
The White House has said the vessel captured on Wednesday was part of a "shadow fleet" used to carry "black market" oil.
Reports have suggested the seizure could be the first of many, with the Trump administration compiling a list of more tankers for possible seizure.
So why is the US now targeting "shadow fleets", and how does it impact the tensions between US President Donald Trump and his Venezuelan counterpart?
What are shadow fleets?
The term refers to fleets of unregulated vessels that aim to bypass sanctions on oil, according to S&P Global.
They're often made up of aging tankers that sail under changing names and flags of countries they are not affiliated with, as well as without required onboard trackers, all to avoid detection.
Valuable cargoes are typically handed off in the middle of the ocean before tankers reach their final destinations.
The 20-year-old tanker seized by the US on Wednesday, currently known as the Skipper, has had a chequered history as part of a shadow fleet.
Previously called the Maera, Toyo and Adisa, it was sanctioned by the US in 2022 for facilitating oil trades that supported designated terrorist organisations Hezbollah and Iran's Islamic Revolutionary Guard Corps.
What suggested the Skipper was part of a shadow fleet?
It was employing multiple evasion techniques.
At the time of capture, the Skipper was falsely flying the flag of Guyana, despite not being registered in that nation, according to the Guyanese government.
The record of the vessel's movements is patchy, too.
All ships above a certain tonnage are required to have a location tracker known as an Automatic Identification System (AIS), according to a UN treaty — a requirement the Skipper was not complying with.
An analysis by maritime intelligence firm Pole Star Defense of the Skipper's movements from November 2024 through November 2025 showed it went 200 days without AIS transmissions.
That included six separate "dark" periods where no location data was shared, with one spanning 83 days.
During those times, the tanker is believed to have passed through known illicit transfer zones and appeared to have conducted cargo operations offshore, "invisible to standard compliance monitoring", the analysis said.
Windward, which uses satellite imagery relied on by US officials mapping the movements of the shadow fleet, reported the Skipper had sailed to China with a cargo of Iranian oil in recent months.
It was also linked to illicit cargoes from Russia.
In late October, Pole Star says the Skipper began spoofing its location data.
Its AIS coordinates placed it off the coast of Guyana at the time, but satellite imagery showed no vessel present at the broadcast location.
Instead, the Skipper was docked at Venezuela's San José Offshore Terminal, loading crude oil.
"This represented an escalation from passive AIS avoidance to active geographic spoofing — an attempt to obscure not just the act of loading, but the specific jurisdiction and origin of the cargo itself," the analysis by Pole Star reads.
Why did the US seize the Skipper?
US Attorney-General Pam Bondi said the decision was made to seize the Skipper because of its alleged involvement in "an illicit oil shipping network" that supported terrorist organisations.
That links back to why the US sanctioned it in 2022.
But the vessel's capture also comes at a time when the US government is mounting a pressure campaign on Venezuelan President Nicolás Maduro Moros.
The Trump administration has for months launched lethal air strikes on boats that it claims are being used to ship illicit drugs, killing more than 80 people.
All the while, the US has built up the largest military presence in the Caribbean Sea in decades and authorised its Central Intelligence Agency (CIA) to begin covert operations inside Venezuela.
The White House has said these operations aim to stop the flow of drugs into the US.
But many, including some in Congress and the Venezuelan president himself, have argued Mr Trump is seeking a regime change.
Stifling Venezuela's oil trade further would ramp up the squeeze on Mr Maduro.
Venezuela's economy is highly dependent on its crude oil trade, which is estimated to make up more than 80 per cent of the country's exports.
A collapse in global oil prices in 2013 caused hyperinflation, food and medicine shortages, and an increase in violence rates.
Democratic senator Chris Van Hollen, a member of the Senate Foreign Relations Committee, said the seizure of the Skipper cast doubt on the government's stated intention to combat drug smuggling.
"This is just one more piece of evidence that this is really about regime change — by force," he said.
Maria Machado, the leader of the US-backed Venezuelan opposition, applauded the Trump administration for weakening the country's already sanctioned oil trade on Thursday.
"The regime is using the resources, the cash flows that come from illegal activities, including the black market of oil, not to give food for hungry children, not for teachers who earn one dollar a day, not to hospitals," she said.
"They use those resources to repress and persecute our people."
Ms Machado intended to challenge Mr Maduro in last year's presidential election but the government barred her from running for office.
Mr Trump said the Skipper was seized for "a very good reason" but did not provide further details.
The US has assembled a target list of more sanctioned tankers for possible seizure, according to a person familiar with the matter who spoke with Reuters.
How is Venezuela's oil trade sanctioned?
The US has for years imposed a suite of sanctions against Venezuela.
That includes measures that threaten to lock out of its economy any American individual or company that does business with the Maduro government.
The first Trump administration blocked Venezuela's access to US financial markets, and in May 2018, expanded them to block any purchase of Venezuelan debt.
The Trump administration has also targeted buyers by introducing 25 per cent blanket tariffs on any country seen to be acquiring Venezuelan oil.
Venezuela's longtime allies Russia and Iran, which are also subject to sanctions, have helped it skirt restrictions by using shadow fleets deployed by shell companies.
What are sanctions?
They are measures governments can take to discourage others from undesirable behaviour without the use of armed forces.
Sanctions can come in the form of financial penalties or restrictions on certain goods, services and commercial activities.
Financial sanctions generally target individuals and can involve freezing their assets or issuing travel bans.
For example, Australia has implemented more than 1,200 sanctions against Russian individuals or entities since 2022 in response to Russia's full-scale invasion of Ukraine.
Restrictions on goods generally prohibit the export or import of those resources with specific countries or regions.
This is the category into which oil sanctions fall.
A key aim of sanctions is to influence the target into changing its behaviour through economic penalties.
Can governments sanction vessels?
Yes — it's even a measure Australia has taken in response to Russia's invasion of Ukraine.
Sanctions can allow governments to direct vessels to leave their nations' waters, even by a particular route, and refuse them entry into a port.
But a nation putting sanctions on vessels doesn't necessarily give it the right to seize them on the high seas.
When is a country legally allowed to seize vessels?
A vessel can be captured on the high seas only in a narrow set of instances, which are: if the vessel is subject to UN Security Council resolutions, considered stateless, not flying a nation's flag, or is a pirate ship.
Windward reported that the Skipper and other vessels sanctioned by the US were vulnerable to interception because they were falsely flagged, making them stateless under international maritime law.
Defence and national security expert Jennifer Parker said Article 110 of the United Nations Convention on the Law of the Sea made clear ships without nationality could be boarded.
"The UN Convention on the Law of the Sea allows any country's navy or coastguard to board stateless vessels on the high seas under Article 110," she told the ABC.
"This provision is routinely used to counter smuggling and other illicit activities at sea.
"Guyana has denied that the vessel is registered under its flag, and the United States would almost certainly have verified this, having tracked the ship for some time. On that basis, the vessel is highly likely to be stateless, making the boarding consistent with international law."
