Prepared by Dick Wildermann
* On April 20, 2010, an explosion on the Deepwater Horizon semisubmersible drilling
rig cause an uncontrolled release of oil and natural gas. Eleven men were killed
and 17 injured by the explosion and fire.
* The drilling rig was located approximately 50 miles offshore Louisiana in water
depths of approximately 5,000 feet.
* On July 15, 2010, the leaking well was capped and a relief well plugged the original
wellbore on September 19, 2010.
* Prior to capping/plugging the well, approximately 53,000 – 62,000 barrels (bbl) of oil
per day (2.23 – 2.60 million gallons) were released from the well, with an
approximate total release of 4.9 million bbl of oil (206,000,000 gallons) over an 87-
* The subsea blowout also resulted in the loss of large quantities of natural gas (to
date this volume is undetermined) (DHUC, 2010).
*Federal court: “BP’s conduct was reckless.” “Gross negligence and willful
* National Commission: The well blowout “could have been prevented.” The
immediate causes “can be traced to a series of identifiable mistakes” by BP and
the operator. BP blamed for “a series of cost-cutting decisions and an insufficient
* BP took short cuts because the well was over budget and behind schedule.
* Flawed decisions (human error) such as:
o using the wrong cement to seal the well;
o failure to monitor properly;
o failure of the crew to detect an increase in pressure that signals loss of well
o BOP failure due to a dead battery.
* More than 6,050 response vessels and approximately 47,850 personnel
responded to protect the shoreline and wildlife and to cleanup coastlines.
* At the surface, approximately 34.7 million gallons (827,251 bbl) of oily water were
recovered and an estimated 11.14 million gallons (265,450 bbl) of oil burned.
* Approximately 1.07 million gallons of dispersants were applied on the surface to
break apart the oil particles, facilitate biodegradation of the oil, and decrease
shoreline impact. In addition, about 771,000 gallons of dispersant were applied
* More than 3.33 million feet of containment boom and 9.7 million feet of sorbent
boom were deployed.
* Approximately 17 percent of the oil was captured through the subsea containment
effort during the spill.
* Of the more than 4,300 miles of shoreline surveyed by NRDA within the first two
years after the spill, approximately 1,100 linear miles were oiled. Approximately
220 miles were heavily oiled and 140 miles were moderately oiled. The remaining
miles of shoreline received light oiling and/or tar balls.
* The oil most severely affected the edges of saltwater and brackish marshes where
oil was stranded for long periods. Sand beaches, barrier islands, tidal mud flats and
mangrove stands also were oiled.
* Approximately 88,500 square miles of Federal waters were closed to
commercial and recreational fishing, approximately 37 percent of the Gulf of
Mexico Federal waters (NMFS, 2010).
* It was estimated that approximately 36 percent of the oil spilled from the Deepwater
Horizon was lost once it reached the water surface due to dissolution,
evaporation, and natural dispersion.
* Winds and waves tore the oil and mousse patches (water-in-oil emulsion) into
smaller pieces, eventually producing tar balls in the form of small, hard, black
pellets. Tar balls can be very persistent in the marine environment and travel long
* During the first two years after the spill, response teams collected over 8,000 live
and dead birds, of which about 1,500 were rehabilitated and released. These birds
represent more than 100 species collected in all five Gulf Coast states.
* Teams also collected over 500 live sea turtles, most of which were visibly oiled.
Almost 90% of these turtles were later released. In addition, over 600 dead turtles
were collected. Sargassum is a vital open water habitat for sea turtles, particularly
juveniles. During the oil spill, sea turtle rescue efforts documented 574 turtles in this
habitat, 464 of them visibly oiled.
* During that same period, almost 200 marine mammals were collected; most were
dead. In 2011, there were 356 strandings of bottlenose dolphins (compared to a
historical average of 74). Many of these animals had visible oil on their bodies.
* As of early 2012, visual observations suggest that two hard-bottom coral
communities have been impacted by the oil spill. At both locations many corals have
been identified as dead or dying. The full extent of injury is still being assessed.
* Ten million user-days of beach, fishing and boating activity were lost.
* The impact on fisheries could total $8.7 billion by 2020.
—The information in this summary came from studies on websites for the National
Oceanic and Atmospheric Administration (NOAA) and the Bureau of Ocean Energy
–Most of the effects information is from: NOAA. April 2012. Natural Resource
Damage Assessment. Status Update for the Deepwater Horizon Oil Spill. Effects were
updated in February 2017 using: Ingrid Biedron, Ph.D. and Suzannah Evans. April
- Time for Action: Six Years After Deepwater Horizon. Oceana.