The blacklisting of individual tankers has been the most effective economic tool used against Russian President Vladimir Putin’s shadow fleet and should be stepped up by the US and its allies, according to a new report.

The US has targeted 41 tankers since October — representing less than 10% of the dedicated Russia fleet — with many of them effectively forced out of commercial trading, according to the KSE Institute, a think-tank linked to Ukraine’s Kyiv School of Economics.