More pressure on oil consumers or a naval blockade – how could the Russian shadow fleet in the Baltic Sea be stopped?

It's the end of August when the "Bosca" pushes its way through the Fehmarnbelt waterway. The tanker is almost 250 meters long and comes from Primorsk, Russia. It sits deep in the Baltic Sea, fully loaded with Russian oil. The flag on the stern has changed five times over the years. The "Bosca" is currently sailing for the landlocked African country of Malawi.

The "Bosca" is a ship of the shadow fleet—a gray area of ​​global shipping. Since the beginning of its war of aggression in Ukraine, tankers like this one have ensured that the Kremlin's war chest remains full. On average, three ships like the "Bosca" transit the Baltic Sea every day, refueling primarily in the Russian ports of Ust-Luga and Primorsk near St. Petersburg.

To get an idea of ​​why it is so important for the West to stop the shadow fleet, it helps to look at the numbers. They can be found in a March publication by the German Federal Agency for Civic Education. According to the report, an average of around 200 loaded shadow tankers leave Russian ports each month. A good three-quarters of all Russian oil exports by ship originate from terminals in the Baltic and Black Seas, the report states . The ships transported around 110 to 120 million barrels per month and brought the Kremlin almost 15 billion euros in additional revenue last year.

This is bitter for the West, but existential for Ukraine. The shadow fleet ensures Russia's war chest is buoyed. And it renders the core element of Western oil sanctions against Russia virtually ineffective. It is therefore urgently time to stop the shadow fleet in the Baltic Sea—or at least make it riskier, slower, and more expensive. There are five ways to do this:

The most effective lever lies not in the water, but on land: with the buyers of the oil and the service providers who secure the transports. So far, Russia has managed to deliver large quantities to India, China, and other countries via its shadow fleet. India is currently pumping itself full of cheap crude oil. For Moscow, this is a financial lifeline; for Delhi, it's a comparative bargain.

The counter-strategy would be to put pressure on the buyer countries. Europe and the US could attach clear conditions to their arms exports, technology deliveries, and market access: no oil from sanctioned tankers. For example, India is seeking closer cooperation with France (Rafale fighter jets) and Germany (submarines, artillery ammunition) on arms deliveries. This would give the two European states leverage against Delhi.

So far, however, it has been primarily the American sanctions that have been effective. Tankers that have landed on the US Treasury Department's blacklist, for example, are immobilized. The reason: oil buyers, involved banks, or port authorities face punishment from the US as soon as they have any dealings with the sanctioned ship. They face the threat of being cut off from the US financial system and the dollar as a means of payment. Hardly anyone can afford that.

The measures certainly had an effect. According to a report by the Federal Agency for Civic Education, in March of this year, 213 tankers were sanctioned by the US, 131 by the EU, and 133 by the UK. The increased pressure on the shadow fleet has led to Russia having to accept further price reductions on its oil exports. This was due to the increased cost of organizing transport capacity, and carriers imposing surcharges to reflect the increased risks.

In the spring, however, doubts arose about the continuation of US sanctions. Media reported that President Donald Trump was examining the extent to which the sanctions could be eased in order to begin peace talks with Russian leader Vladimir Putin. However, Putin has so far shown no signs of engaging in such talks. There is no indication so far that Trump is sticking to the plan.

Another tool in scenario one would be a unified blacklist. Currently, there is no consolidated database that compiles names, IMO numbers, flags, insurers, and images of ships. The IMO is the International Maritime Organization. If such a list were maintained and regularly updated by the EU, the UK, the Nordic, and the Baltic states, it could be fed directly into port and coastal protection systems. Shipping companies, banks, and insurers could no longer claim ignorance.

The effect would be quite painful for Moscow. The gray area in which the ships could operate would become narrower, and the shadow fleet would become more expensive. Every ship discovered, every docking denied, and every bank that blocks payments increases the costs for the Kremlin.

A ship's passage can only be restricted in exceptional circumstances. This is stipulated by the International Convention on the Law of the Sea. A feared environmental disaster or a violation of the International Maritime Organization's guidelines is usually not sufficient grounds for this. However, there is scope for maneuver when it comes to safety and environmental issues. Insurance is one lever.

Since the end of 2024, the Nordic and Baltic states have been checking whether tankers are adequately insured. This happened in Finland in December 2024, when the tanker "Eagle S" was stopped, and in April of this year with the "Kiwala," which was moored by Estonia. The model could be tightened by requiring the presentation of valid P&I insurance when entering the Baltic Sea from the North Sea.

P&I stands for "protection and indemnity." This primarily refers to adequate financial coverage in the event of an oil spill. Experts doubt that the ships of the shadow fleet have adequate insurance, or that this is monitored by the flag states. Past oil spills have shown that the damage can run into the billions. If a ship refuses to provide information or if the insurance proves inadequate, sanctions may be imposed. This can go as far as the ships being decommissioned or confiscated by the authorities.

To date, the situation in the Baltic Sea has primarily been based on a military assessment. NATO has consolidated its activities under German leadership. Coordination in the civilian sector is lacking. Germany, for example, divides coastal protection among customs, the Federal Police, the Waterways and Shipping Administration, and the Federal Office for Agriculture and Food. There is no unified coast guard. Accordingly, rapid response chains are lacking.

The solution would be a joint civilian situation center for the Baltic Sea states, possibly jointly or closely coordinated with the military. This is likely to attract criticism in Germany. They consider a combination of civilian and military measures unconstitutional. But Russia is doing exactly that: It is operating in the Baltic Sea with a mixture of civilian and military measures.

Therefore, a joint situation center for the military and security authorities would be crucial. Satellite images, drone images, low-level helicopter approaches to suspicious vessels, radar, underwater reconnaissance, and financial data could be combined to keep an eye on every vessel. Anomalies such as sudden turns, unusual speeds, and failures of the automatic identification system (AIS) could be detected immediately. Only then would targeted boardings—the boarding, search, and detention of a vessel by security authorities—be possible.

For Germany, this would mean establishing a coast guard with clearly defined responsibilities. Security experts have been calling for this for years, but its implementation has stalled due to wrangling over responsibilities between the federal and state governments, as well as between individual agencies.

For the Baltic Sea region, this would mean creating a joint control center where Sweden, Finland, the Baltic states, Poland, Denmark, and Germany exchange data. This would allow evidence to be secured across borders, and the boarding of a ship, for example, could be upheld in the event of a lawsuit before the International Tribunal for the Law of the Sea.

This would have a twofold benefit: Firstly, it would prevent environmental disasters caused by wrecked rusty tankers. One example is the tanker "Eventin," which ran aground off Rügen in January of this year and was seized by German customs. Secondly, it might have a deterrent effect, because every ship in the shadow fleet would be aware that it is under surveillance.

Since January of this year, NATO warships from the "Baltic Sentry" mission have been patrolling the Baltic Sea. This mission is primarily intended to protect underwater pipelines and data cables. There have been repeated cases of cables and lines being destroyed by suspected sabotage. At the same time, NATO has increased its presence at sea and in the air, making it easier to monitor suspicious vessels.

In addition, there could be an EU deployment comparable to the "Aspides" mission in the Red Sea. Its purpose is to monitor freedom of sea routes. But this also carries risks. Russia, which sees itself at war with the West, could view any increased presence of Western ships as an escalation. The problem: The military capabilities of the Baltic Sea states, not least Germany, are barely sufficient to sustain such a mission for years. The signal value, however, would be enormous: Europe protects its sea routes – and will not tolerate shadow fleets in sensitive waters.

This scenario is the least likely. A naval blockade to prevent the shadow tankers from passing through could only be established in a state of defense. Otherwise, the right to peaceful and free passage applies to every ship. In plain language: Germany and other Western countries would have to declare a state of defense so that they could block the straits around Denmark and Sweden with military vessels. This, however, would massively increase the likelihood of an armed conflict with Russia.

The Union's foreign and security policy expert, Roderich Kiesewetter, says that the Baltic Sea is indeed the "battlefield in Russia's shadow war" against the West. Therefore, according to Kiesewetter, it may be legitimate, within the framework of the right of self-defense, to declare a state of tension and have the navy take action against the shadow ships.

However, according to Kiesewetter, Germany would need the support of other states to achieve this, perhaps within the framework of a coalition of the willing. A complete blockade, meanwhile, would only be possible in a state of defense. Furthermore, it is much more important to inspect the ships for compliance with safety standards and insurance coverage. In the event of non-compliance, Kiesewetter continued, further voyage could be prevented entirely legitimately.

Russia's shadow fleet is a symbol of the gray zone of war. Neither sanctions nor naval presence alone are sufficient to significantly impact the Kremlin's oil revenues. Only combined with pressure on buyers, strict controls at the straits, a civil situation report, and a military presence could the risk for Russia presumably be increased and profits reduced.

The goal would not be a total blockade of the Baltic Sea, but rather to dry up the gray zone. More expensive, riskier, slower—that alone could cost Russia billions—and possibly shorten the war in Ukraine.