North Korea may be jerry-rigging cargo vessels to illegally transport refined petroleum, filling ballast tanks with oil instead of water and using concrete to steady ships in rough seas, according to a forthcoming U.N. Panel of Experts report.

An unnamed U.N. member state provided “preliminary information” on the unorthodox and likely dangerous practice to sanctions monitors, a draft of the report seen by NK News shows. The revelation may help explain relatively stable fuel prices in the DPRK despite fewer observed oil deliveries.