Marine oil water separator equipment has been a shipboard requirement since the 1970’s, but recently it has become evident that oil water separators have not been as effective as had been assumed. Actual and alleged improper operation  of this equipment by shipboard crews has resulted in criminal prosecutions of engine room crew members in the United States.

Oily bilge water is almost an unavoidable product in ship operations. Bilge water that is generated in proximity to shipboard equipment (such as in the engine room) often contains oil. Direct discharge of this water would result in undesirable transfer of waste oil to the marine environment. By international agreement under the MARPOL convention, most commercial vessels need to be fitted with an oily water separator to remove oil contaminants before bilge water is pumped overboard. Overboard oil discharge is illegal.