At least five tankers from Russia's so-called "shadow fleet" have leaked oil into European waters over the past year, according to an investigation by Politico and SourceMaterial. The vessels, used to evade Western sanctions, continue to operate largely unchecked, reports the Moscow Times.

The investigation cited satellite imagery from SkyTruth and shipping data from Kpler showing oil slicks near European coastlines. Two of the tankers were already under British sanctions when the leaks occurred.

Latvian Energy Minister Kaspars Melnis called the incidents "a huge problem," warning that Europe has been fortunate to avoid a major environmental disaster. The British Foreign Office described the fleet as "a desperate and dangerous attempt" by President Vladimir Putin to maintain oil revenues.

The shadow fleet consists of ageing tankers with unclear ownership and no insurance, deployed after G7 nations imposed a price cap on Russian oil exports in response to the 2022 invasion of Ukraine. Oil revenues make up about one-quarter of Russia's federal budget.

Lloyd's List Intelligence estimates the fleet now includes around 1,300 vessels. Their operations have also been linked to damage to underwater infrastructure in European waters.

The European Union has blacklisted 444 tankers from EU ports and insurance services, while Britain has sanctioned about 450 ships. Melnis said the effectiveness of current sanctions remains uncertain.

Experts told Politico that many of the vessels are in poor condition and operate outside regulatory oversight, raising the risk of catastrophic spills. The Center for Research on Energy and Clean Air estimates cleanup costs for a major spill could reach EUR1.4 billion (US$1.5 billion), likely to be borne by European taxpayers if ownership cannot be traced.