The US Treasury is intensifying its hunt for vessels and shipping companies violating sanctions on Russian oil exports, sanctioning 3 tankers and their operators on Thursday. The Treasury is also investigating around 30 ship management companies covering 100 vessels on suspicion of violating the oil price cap on Russian crude. It has sent warning letters requesting documentation. Identifying sanctions violators is complicated by the murky ownership structures of shipping companies and the use of intermediaries in oil trades. Around 30% of Russian oil exports from European ports still use vessels with EU ownership.