Respondent is an oil and gas exploration and production company in the Gulf of Mexico operating an offshore lease in Mississippi Canyon Block 725. The TransOcean Deepwater Horizon drilling ship experienced high waves in a tropical storm and an emergency riser disconnect occurred. The riser is the umbilical from ship to sea floor. Approximately 1817 barrels of synthetic based drilling mud was discharged from the riser onto the sea floor as a result of the disconnect.