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.

According to the member state, the technique involves using ballast tanks and cargo holds as makeshift oil