Drilling fluid barite contains trace quantities (< 1 mg/kg) of mercury. Environmental research  conducted over a period of more than two decades has shown that the mercury in drilling fluid barite has very limited bioavailability to marine organisms.  Nonetheless, the presence of mercury in drilling wastes remains a subject of interest in environmental assessments of offshore drilling activities.  This presentation will review what research tells us about the amounts of mercury in barite, its chemical form in barite, and its fate in the marine environment. Overall, the available evidence supports the conclusions that mercury associated with drilling-fluid barite: (1) is mainly present in metal sulfides with very low solubility, (2) is not detectably leached into seawater, and (3) has limited availability to marine organisms.