Spills ≥ 50 Barrels (2,100 gallons) – 2010***

April 7, 2010 – Statoil Gulf of Mexico LLC

Remarks: On April 7, 2010 at 1600 hours the "Maersk Developer" rig personnel decided to circulate the well to condition the mud. During circulation approximately 125 barrels of Synthetic Based Mud (SBM) was spilled overboard through a dump valve located approximately 20 feet below the waterline. Once the SBM was discharged overboard, it was discovered that the shakers were inadvertently lined up to the shaker dumps and then overboard for drilling out cement and cement cuttings. The valving set-up was not properly configured to go from the shakers to the MI Swaco unit for circulating the mud weight. In addition, there was no written procedure discussed or work permit completed prior to conditioning the mud during circulation.

Accident Investigation Report: Form 2010 7-April-2010 WR543

NRC Report: 936437

April 20, 2010 – BP Exploration & Production Inc.

Remarks: A loss of well control, explosion, and fire on the Deepwater Horizon Mobile Offshore Drilling Rig Unit (MODU) resulted in 11 fatalities and lost-time injuries to 46 persons. The incident also resulted in the release of crude oil until the well was capped on July 15, 2010. This incident is currently under investigation by a BOEMRE/USCG Marine Board of Investigation that is co-chaired by U.S. Coast Guard and BOEMRE (Bureau of Ocean Energy Management, Regulation and Enforcement. Information on the status of the investigation can be found at the Joint Investigation Website.

Deepwater Horizon Website: http://www.restorethegulf.gov/

May 13, 2010 – Shell Offshore Inc.

Remarks: The operator on the Green Canyon A-Brutus tension leg platform started methanol injection in the morning of 5/12/2010 to equalize valves on the G4 subsea well. Pump discharge pressures indicated the methanol was not making it to the tree. Through troubleshooting over time it was determined there was an external or internal leak on the subsea umbilical. The methanol injection was shutdown and an ROV was used to inspect the lines where a leaking fitting was found on a hub. The estimated total release was 122.7 bbl of methanol prior to securing the leak. The cumulative time was about 7 hours.

NRC Report: 940115

December 1, 2010 – Stone Energy Corporation

Remarks: During operations to transfer mud from the active pit to reserve pit in order to clean the active pit, the driller noticed losses during the pumping operations which exceeded the expected losses, and the pumps were shut-down. It was discovered that the crossover line from the reserve mud pit to the active mud pit used to transfer the mud from the pump was tied into the pit dump line. The dump line had been opened to wash out the pit-lines which were tied into the charging pump lines as well as the dump line which had valves open. This caused the mud to travel to the active pits then into the overboard shunt line, allowing mud to flow into the Gulf of Mexico, 25 feet below the surface of the water.

NRC Report: 961093

October to December 2010 – Taylor Energy Corporation

Remarks: The Mississippi Canyon 20, Platform A, an 8-pile fixed structure was installed in Federal waters in 1984. It was destroyed in September 2004 by Hurricane Ivan. Approximately 61.54 bbls seeped from the structure between October 1 to December 31, 2010.

NRC Report: Daily overflights are being conducted at this location and observations are being reported to NRC

*** The summary for a Chevron Natural Gas Pipe Line Company spill that occurred on March 25, 2010 at SS 157 has been removed from this page because the final volume of the spill was determined to be 5.95 bbls (less than 50 bbls).

*** The summary for a Mariner Energy spill that occurred on September 29, 2010 at EB 164 has been removed from this page because the final volume of the spill was determined to be 6.5 bbls (less than 50 bbls).

One Barrel (bbl) Equals 42 U.S. Gallons (gal)

Synthetic Oil Fluids*: In deepwater drilling, synthetic-based muds (SBM’s) are preferred over petroleum oil-based muds (OBM’s) due to the SBM's superior performance properties. The synthetic oils used in SBM’s are relatively non-toxic to the marine environment and have the potential to biodegrade.

60%**: Indicates that for a synthetic-based mud release, the exact percentage of volume of synthetic base oil to total volume of mud released was not available and 60% was used as a reasonable approximation.