Slop oil, which may consist of residues and upstream products from refineries, which do not meet the specifications with regard to water and salt content as well as oils from leakages for instance. In many oil-producing countries, for instance in South America, in the Middle East or in Russia, the common practice for many decades has been to pump these contaminated oils into lagoons or intermediate storage; these lagoons are each capable of storing up to one million barrels of oil. The lagoons frequently hold an undefined mixture of oil, water and sediments. The water content can vary between 10 and 70 percent, as can the oil content, and the solids content can range between 3 and 15 percent. Everything is conceivable, from a relatively aqueous low-viscosity mixture right through to substances which are similar to tar with a viscosity of more than 1000 Centistokes.