The Russian shadow fleet remains one of the main tools for circumventing Western sanctions, and also poses a threat to the environment, maritime safety and critical infrastructure. In response, EU Member States, along with Iceland, Norway and the United Kingdom, have adopted a comprehensive approach to curbing its activities, combining legal, regulatory and military instruments. The main transport routes for Russian oil pass through the maritime zones of Denmark, Estonia, Finland, Germany, Norway, Sweden and the United Kingdom, with varying levels of traffic. Since 2025, maritime interventions have steadily increased, including boarding by authorised personnel or the seizure of a vessel (detention or confiscation). Seizure results in the vessel being placed under the control of the competent authority, stripping the shipowner or crew of the ability to operate it or dispose of its cargo.

Results

The application of the law of the sea to stateless vessels or those flying an invalid or false flag has become an important tool for European states. In 2025, the NB8++ states (Belgium, Denmark, Estonia, Finland, France, Germany, Iceland, Latvia, Lithuania, the Netherlands, Norway, Poland, Sweden, and the United Kingdom) made combating these vessels in the Baltic and North Seas a priority, and the EU confirmed the possibility of taking measures against them as provided for under international and national law. In 2025, High Representative Kaja Kallas appointed Polish national Maciej Stadejek as special envoy to counter the Russian shadow fleet, and in 2026, EU diplomats began talks with the flag states that register vessels in this fleet to facilitate inspections on the high seas. The mandates of two EU military operations were also extended: Operation IRINI in the Mediterranean and Operation Atalanta in the Red Sea and the western Indian Ocean, enabling the inspection of shadow fleet vessels through boarding at sea (though neither has the authority to detain ships in EU ports).

The impact of these interventions has grown alongside G7+ diplomatic pressure on “flag of convenience” states—including Panama, Barbados and Cameroon—to deregister sanctioned vessels. As a result, in 2025, the number of vessels operating without a valid nationality increased (from 15 in December 2024 to 138 in July 2025, according to the CREA), thereby making it possible to detain them. This was facilitated by the expansion of EU and NATO monitoring systems, the launch of NATO’s Operation Baltic Sentry in 2025, and an increase in the number of maritime patrols.

As a result, between December 2024 and August 2026, several countries—primarily France and Sweden—and the forces involved in Operation IRINI carried out 18 interventions or attempted interventions against oil tankers (see table), most of which were suspected of not flying a valid flag. These actions mainly resulted in temporary detention in port, financial penalties and proceedings against the captains. The pressure yielded tangible results. Some tankers began to opt for longer routes to minimise the risk of inspection. Following the United Kingdom’s detention of the Smyrtos in June 2026, some vessels began to bypass the UK’s exclusive economic zone, whilst part of the traffic was seasonally diverted to the Arctic route. Meanwhile, inspections in the Mediterranean and the threat of Ukrainian attacks prompted some tankers to use the route around Africa. Despite these changes, Russia continues to maintain significant tanker traffic through the Baltic and North Seas, which account for approximately 40 per cent of Russian oil and petroleum product shipments (data from the Kyiv School of Economics, July 2026).

Russia’s response

The Russian authorities portray the detention of vessels as a violation of international law and acts of economic warfare on the part of the West. They have also begun to raise challenges against European practices at the International Maritime Organisation. In addition to changing oil transport routes, Russia has increased the number of vessels sailing under its own flag. Many vessels replace their false registrations with legitimate, albeit less credible, flags—such as those of Equatorial Guinea or Sierra Leone—before entering European waters. According to Windward, in July this year, for the first time, no vessel without a valid flag loaded oil at Baltic ports. In the year to July 2026, the number of vessels flying a false flag fell from 138 to 48 (CREA data).

Russia has also declared its readiness to take retaliatory action against countries involved in the detention of Russian merchant vessels. At the same time, it has stepped up the protection of maritime transport. The Russian Navy maintains a constant presence on the routes used by the shadow fleet, and there are increasingly frequent reports of oil tankers being escorted by Russian aircraft and warships. Between 2025 and 2026, British vessels monitored 89 Russian vessels, including 61 military ones, whilst the Russian Navy’s activity in British waters increased by around 30 per cent over these two years. In 2026, Estonian authorities detected machine-gun emplacements on the gas carrier Marshal Vasilevskiy, owned by Gazprom. Some shadow fleet vessels are protected by additional guards, presumably armed.

However, experience to date suggests that Russia’s ability to directly prevent such detentions is limited. The only one example was in May 2025, when the Estonian authorities refrained from detaining the tanker Jaguar due to its Russian escort. Nevertheless, such demonstrations of force increase the political and operational costs of such actions, discouraging some states—particularly Estonia—from making more active use of this instrument.

Barriers

The effectiveness of these measures is limited primarily by the lack of a unified approach among European states, as only some of them actively detain vessels in ports (see table). Most rely on monitoring and checks of documents and insurance. The absence of common practice leads to a diversion of traffic. Temporary detentions of vessels in one body of water result in part of the shadow fleet being diverted to the waters of countries applying less restrictive measures. This was confirmed by the increase in tanker traffic near the German coast in 2026, following Sweden’s detention of several vessels.

The cost of detentions also remains a problem. The state must provide a berth, supervision and vessel services. Although some of the costs may be recovered from the owner or operator, opaque ownership structures often make this difficult. The environmental risk associated with potential oil spills whilst a vessel is detained or at berth also remains a burden. There is a lack of data to enable estimates of the full costs of such operations; however, the experiences of Belgium and France indicate that partial reimbursement of expenses is possible.

Restrictions also arise from international law. Under the United Nations Convention on the Law of the Sea, the detention of a vessel is temporary in nature, and once certain conditions are met, the vessel should be released. Whilst inspections at sea or temporary detentions are relatively easy to carry out, the permanent seizure of a vessel and its cargo requires a much stronger legal basis. The proceedings are lengthy and complex, and to date only Swedish courts have authorised the transfer to Ukraine of a detained vessel used in the illegal trade in Ukrainian grain.

Conclusions and recommendations

Interventions to date against shadow fleet vessels have increased the costs of its operations, restricted its operational freedom and raised the risks associated with Russian oil exports. However, they have not led to a lasting reduction in this practice. Due to legal barriers and the risk of escalation, a military blockade of the shadow fleet remains unlikely. A more realistic solution—in addition to strengthening sanctions and regulatory measures—is to increase the number of inspections and detentions carried out in accordance with the law of the sea. Closer coordination of actions between the states of the Baltic and North Sea regions, and the development of joint operations, would be of key importance to enforcing the sanctions regime. This could be complemented by the establishment of a specialised EU maritime operation responsible for inspecting and detaining shadow fleet vessels. Strengthening the security and resilience of critical maritime infrastructure through the development of defence, reconnaissance and monitoring capabilities should remain a priority for Poland. Poland could also initiate work on a regional maritime security convention for the Baltic Sea, to establish a clear legal basis for the control and detention of vessels posing a threat to shipping, critical infrastructure or the environment.