Law of the Sea comes to life in the hunt for sanctioned Russian oil 

Until US President Donald Trump reversed the thrust of his sanctions policy of Russian oil on Friday, Ukraine’s Western allies had been ramping up the use of international law.

Countries sanctioning Russian oil have for the first time enforced boarding and inspection rights under the Law of the Sea this year, experts told Al Jazeera.

“The whole idea now is to disrupt, deter and make it more expensive and costly for Russia to logistically get their oil to market on these ships, and that’s definitely happening,” said Michelle Bockmann, an analyst at maritime intelligence company Windward.

Some Russian officials believe worse is to come.

“Western countries are trying to organise the interception of our vessels. London and Brussels are drawing up plans to blockade the Baltic Sea and the straits leading into it. Other key shipping routes are also under threat,” Russian Maritime Board chairman Nikolai Patrushev told officials during a visit to China on October 12.

Western sanctions not only ban Russian oil purchases in the sanctioning territories. They forbid Western-insured tankers from selling Russian oil to third parties except at below-market prices, which leaves Russia with little or no profit.

Since sanctions were imposed in 2022, Russia has been exporting about half of its crude oil through a “shadow fleet” of tankers that are not owned or insured by Western institutions, and often do not comply with environmental and safety standards.

It is the right to enforce these standards that allows the United States, United Kingdom and European Union to step up compliance inspections using Article 110 of the United Nations Convention on the Law of the Sea (UNCLOS), which allows coastal states to inspect vessels.

That has decreased Russia’s room for manoeuvre in its cat-and-mouse game of circumventing oil sanctions 45 months after the EU, US and other Group of Seven (G7) states imposed them.

“A lot of these ships were using fraudulent registries, and they were stateless,” said Bockmann. Under UNCLOS, she said, “Instead of just hailing them, ‘Hey, what’s your flag? What’s your insurance?’ and then letting them merrily go on their way under the right of innocent passage … they now had a legal basis to board them.”

Shadow tankers have engaged in various illegal practices that exposed them to suspicion and boarding. They have transferred Russian oil from one vessel to another on the high seas to disguise its provenance. They have turned off their trackers to avoid monitoring, falsified their positions, evaded insurance obligations, and flown false flags.

The catalyst for using Article 110 against these practices was the US, which invoked it late last year to board vessels evading US Department of the Treasury sanctions against the export of Venezuelan oil in Operation Southern Spear.

With help from the UK, US Marines seized the Russian-owned Bella I, sanctioned for carrying Iranian and Venezuelan as well as Russian oil, in the North Atlantic last January.

The UK and France have since boarded several other vessels under UNCLOS rules. Although these inspections are few compared to the hundreds of shadow tankers afloat, they have put pressure on the shadow fleet, experts said.

“Article 110 had just been sitting there, not really getting any traction,” said Kristina Siig, a professor of economic law at Aalborg University in Denmark. “The tool has always been there, but it just never got pulled out of the drawer.”

This new adherence to law has had knock-on effects in the shipping industry.

“Due diligence has become the biggest headache in ship management,” said George Xiradakis, a maritime consultant who sits on the boards of several shipping companies in Piraeus, Greece.

Ship charterers and buyers “have to check thoroughly that a ship is in compliance with international standards”, he told Al Jazeera, noting, “The time requirement compared to 2025 has gone up by a factor of several times manyfold.”

The sanctioning nations have pursued the shadow fleet relentlessly.

After being evicted from Western fleets, Russia turned to flags of convenience. The EU, UK and US approached those registries and persuaded them to oust the shadow vessels.

“St Kitts and Nevis were the very first ones in early 2024 … Palau, Gabon, Gambia, Cook Islands, San Marino, Barbados, Comoros, Guinea-Bissau, Sao Tome – they’ve all stopped,” said Bockmann.

Russia reacted this year by bringing many of those tankers onto its own registry.

TankerTrackers.com lists 340 dark or shadow tankers as Russian-flagged. Sanctioning states have responded by using UNCLOS.

Zelenskyy’s ‘sanctions’

Ukraine wants to see all of Russia’s export revenue from fossil fuels dry up, and its President Volodymyr Zelenskyy has warned that Trump’s rapprochement with Moscow will prolong the four-and-a-half-year Russia-Ukraine war.

Kyiv has this year struck at least 26 of Russia’s 30 refineries, causing headaches on the global market.

Russia saw an initial windfall of 31 billion euros ($35bn) this year, after the crisis over the blockage of the Middle East’s Strait of Hormuz raised oil and gas prices worldwide, the Centre for Research on Energy and Clean Air (CREA) calculated.

That windfall temporarily bucked a trend of constantly falling Russian oil and gas revenue since the Ukraine war began in 2022. Month-on-month revenues shot up by 52 percent in March.

But Russia’s August revenue from crude oil, refined products and gas all fell by eight percent, following a 12 percent drop in July and a one percent drop in June.

The binary weapon of UNCLOS and national law

The official rationale for inspections is safety, and under UNCLOS “we have a right, we actually have a joint obligation, to try to help each other to police that”, said Siig.

But the agenda that drives these inspections – stopping Russia’s war of aggression in Ukraine by interdicting the Russian oil trade – is not enforceable under UNCLOS, she said.

“We are not allowed to tell certain states that they can’t export goods. The only entity that can do that is the UN,” she said. “To enforce sanctions, you have to have state jurisdiction.”

That combination of national and international law makes Denmark and Sweden extremely important.

Together, they control the narrowest chokepoints in the Baltic, where shipping has to pass to enter the North Sea and the Atlantic. So tankers loading crude oil and petroleum products at the Ust-Luga and Primorsk refineries in the Leningrad region have to pass through Danish and Swedish territorial waters, where national laws fully apply, to reach global markets.

The Danish Maritime Authority recorded 292 Russian shadow tanker transits through the Baltic in 2025, and it has progressively tightened its inspection regime. In February 2025, Danish authorities began compliance inspections on tankers anchored off Skagen, and in April detained the Vietnamese-flagged shadow tanker Vigo after finding its fire safety lax.

In October, Denmark broadened inspections to include ballast systems, fuel quality, emissions, waste management and certificate verification.

“The Danish approach has been to throw the book at [Russia],” said Siig, as Danish authorities now ask for an oil insurance certificate, a sail plan through the Danish Straits and safety documents in addition to an insurance certificate, she said.

Russia ‘acting aggressively towards NATO’

Conscious of the danger of being bottled into the Baltic, Russia has reacted with fury.

On September 14, a Russian frigate fired two flares at a Danish helicopter that was inspecting it in international waters south of Gedser, in the Danish Straits.

“Russian forces are increasingly acting aggressively towards NATO military units in the Baltic Sea region,” said a recent Danish Defence Intelligence Service report. “Russia is under more pressure than it has been at any other point during the war against Ukraine. Ukraine’s sustained long-range attacks are causing still more extensive damage deep inside Russia … The Russian economy is on the brink of a major crisis, driven by military expenditures, international sanctions and Ukrainian strikes.”

Denmark is treading carefully as it flexes these provisions of international law for the first time, said Siig. Danish authorities may now be asking for an oil insurance certificate, safety documents, a sail plan through the Danish Straits, and an insurance certificate, but closing off the Strait is not on the cards, she said.

“I have seen no public evidence that such a measure is being considered. Under the ordinary Law of the Sea regime, the Danish Straits are international straits subject to transit passage, and the Kingdom of Denmark has a strong interest in preserving that rules-based system,” Siig said.

“Russia has lost the Baltic,” she noted. “Everybody seemed to be getting along just fine. Then Ukraine happened, and suddenly they got boxed in, geopolitically.”

Ukraine has asked its allies to enforce sanctions even more forcefully. That, said Siig, “might stop the Ukrainian war, and it might start a new one”.