Law of the Sea invoked in hunt for sanctioned Russian oil tankers

Until US President Donald Trump reversed course on sanctions targeting Russian oil on Friday, Ukraine's Western allies had been steadily ramping up their use of international law to squeeze Moscow's oil exports.

According to experts who spoke to Al Jazeera, countries imposing sanctions on Russian oil this year exercised for the first time their right to board and inspect vessels under the United Nations Convention on the Law of the Sea (UNCLOS).

"The idea now is to disrupt, deter and make it much more logistically costly for Russia to get oil to market using these ships, and that is certainly happening," said Michelle Bockmann, an analyst at maritime intelligence firm Windward.

Some Russian officials believe worse lies ahead. "Western countries are trying to organise the interception of our ships. London and Brussels are drawing up plans to blockade the Baltic Sea and the straits leading into it. Other important shipping routes are also under threat," Nikolai Patrushev, chairman of Russia's Maritime Board, told officials during a visit to China on October 12.

Western sanctions do not only ban buying Russian oil within sanctioning jurisdictions. They also bar tankers insured by Western firms from selling Russian oil to third parties unless it is priced below market levels, leaving Russia with little or no profit.

Since the sanctions were imposed in 2022, Russia has exported roughly half its crude oil through a "shadow fleet" — tankers neither owned nor insured by Western entities, and which often fail to meet environmental and safety standards.

Enforcing those standards allows the United States, Britain and the European Union to step up compliance inspections under Article 110 of UNCLOS, which permits coastal states to inspect vessels.

This has narrowed Russia's room to manoeuvre in a cat-and-mouse game to evade oil sanctions, 45 months after the EU, the US and other G7 nations imposed them.

"A lot of these ships use fake registrations and have no nationality," Bockmann said. Under UNCLOS, she said, "instead of just calling them up and saying, 'Hey, what's your flag? What's your insurance?' and then letting them happily continue their journey under the right of innocent passage... now they have legal grounds to board."

Shadow fleet vessels have carried out numerous illegal practices that have drawn suspicion and led to boarding and inspection. They transfer Russian oil from ship to ship on the high seas to disguise its origin. They switch off tracking devices to avoid surveillance, falsify positions, evade insurance obligations and fly false flags.

The catalyst for using Article 110 against such practices was the United States, which invoked the provision late last year to board ships evading US Treasury sanctions on Venezuelan oil exports under Operation Southern Spear.

With British support, US Marines seized the Russian-owned tanker Bella I — sanctioned for carrying Iranian, Venezuelan and Russian oil — in the North Atlantic in January.

Britain and France have since boarded and inspected several other vessels under UNCLOS rules. Although these inspections remain few compared with the hundreds of shadow fleet ships in operation, they have put pressure on the fleet, experts say.

"Article 110 was already there, not really being used," said Kristina Siig, a professor of economic law at Aalborg University in Denmark. "The tool has always existed, but it had never been taken out of the drawer."

This newfound legal compliance has had knock-on effects across the shipping industry.

"Due diligence has become the biggest headache in ship management," said George Xiradakis, a maritime consultant and board member at several shipping companies in Piraeus, Greece. Charterers and buyers "have to scrutinise thoroughly that the ship complies with international standards," he told Al Jazeera, noting that "the time required compared with 2025 has increased many times over."

Sanctioning countries have relentlessly pursued the shadow fleet. After being shut out of Western fleets, Russia turned to flags of convenience. The EU, Britain and the US approached those registries and persuaded them to strike shadow fleet vessels from their books.

"St Kitts and Nevis were the first in early 2024... Palau, Gabon, Gambia, the Cook Islands, San Marino, Barbados, Comoros, Guinea-Bissau, Sao Tome — they have all stopped," Bockmann said.

Russia responded this year by adding many of those ships to its own registry. TankerTrackers.com lists 340 shadow or murky tankers flying the Russian flag. Sanctioning countries have hit back by using UNCLOS.

Zelenskyy's sanctions

Ukraine wants all of Russia's fossil fuel export revenue drained, and President Volodymyr Zelenskyy has warned that Trump's rapprochement with Moscow would prolong the four-and-a-half-year Russia-Ukraine war.

Kyiv has struck at least 26 of Russia's 30 oil refineries this year, causing disruptions on global markets.

Russia reaped an initial windfall of 31 billion euros ($35 billion) this year after congestion in the Middle East's Strait of Hormuz pushed global oil and gas prices higher, according to calculations by the Centre for Research on Energy and Clean Air (CREA).

The windfall temporarily reversed a steady decline in Russia's oil and gas revenues since the war in Ukraine began in 2022. Monthly revenues rose 52 percent in March.

But Russia's August revenues from crude, refined products and gas all fell 8 percent, following declines of 12 percent in July and 1 percent in June.

UNCLOS and national law: a binary weapon

The stated reason for the inspections is safety, and under UNCLOS "we have the right, indeed a general obligation, to try to help each other enforce that," Siig said.

But the goal driving the inspections — ending Russia's war of aggression in Ukraine by cutting off its oil trade — cannot be enforced under UNCLOS, she said.

"We are not allowed to tell certain countries that they cannot export goods. The only entity that can do that is the United Nations," she said. "To enforce sanctions, you need national jurisdiction."

The combination of national and international law makes Denmark and Sweden critically important.

Together they control the narrowest bottlenecks in the Baltic that ships must pass through to reach the North Sea and the Atlantic. So crude and product tankers at the Ust-Luga and Primorsk refineries in the Leningrad region must transit Danish and Swedish territorial waters, where national law fully applies, to reach global markets.

The Danish Maritime Authority recorded 292 transits of Russian shadow fleet vessels through the Baltic in 2025, and it has gradually tightened its inspection regime. In February 2025, Danish authorities began compliance checks on ships anchored off Skagen, and in April they detained the Vietnamese-flagged shadow tanker Vigo after finding loose firefighting systems.

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

"Denmark's approach is to apply the law rigorously with [Russia]," Siig said, as Danish authorities now require oil insurance certificates, voyage plans through the Danish straits and safety documentation beyond insurance certificates.

Russia 'behaving aggressively towards NATO'

Aware of the risk of a Baltic blockade, Russia has reacted angrily. On September 14, a Russian frigate fired two flares at a Danish helicopter inspecting it in international waters south of Gedser, in the Danish straits.

"Russian forces are increasingly behaving aggressively towards NATO military units in the Baltic Sea region," according to a recent report by the Danish Defence Intelligence Service. "Russia is under greater pressure than at any other point in the war against Ukraine. Ukraine's sustained long-range strikes are causing growing damage deep inside Russia... The Russian economy is on the brink of a major crisis, due to military spending, international sanctions and Ukrainian attacks."

Denmark is acting cautiously as it invokes these provisions of international law for the first time, Siig said. Danish authorities can now demand oil insurance certificates, safety documents, voyage plans through the Danish straits and insurance certificates, but closing the straits is not planned, she said.

"I have seen no public evidence that such a measure is under consideration. 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 maintaining that rules-based system," Siig said.

"Russia has lost the Baltic," she observed. "Everyone seemed to be living in harmony. Then Ukraine happened, and suddenly they are geopolitically encircled."

Ukraine has called on its allies to enforce sanctions even more forcefully. That, according to Siig, "could end the war in Ukraine, and could also start a new one."