<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The Deepwater Horizon drilling rig explosion was the April 20, 2010, explosion and subsequent fire on the Deepwater Horizon semi-submersible Mobile Offshore Drilling Unit (MODU), which was owned and operated by Transocean and drilling for BP in the Macondo Prospect oil field about 40 miles (60 km) southeast off the Louisiana coast . The explosion and subsequent fire resulted in the sinking of the Deepwater Horizon and the deaths of 11 workers; 17 others were injured . The same blowout that caused the explosion also caused a massive offshore oil spill in the Gulf of Mexico, considered the largest accidental marine oil spill in the world, and the largest environmental disaster in U.S. history . </P> <P> The $560 million platform was built by Hyundai Heavy Industries in South Korea and completed in 2001 . It was owned by Transocean, operated under the Marshalese flag of convenience, and was under lease to BP until September 2013 . At the time of the explosion, the Deepwater Horizon was on Mississippi Canyon Block 252, referred to as the Macondo Prospect, in the United States sector of the Gulf of Mexico, about 41 miles (66 km) off the Louisiana coast . In March 2008, the mineral rights to drill for oil on the Macondo Prospect were purchased by BP at the Minerals Management Service's lease sale . The platform commenced drilling in February 2010 at a water depth of approximately 5,000 feet (1,500 m). At the time of the explosion the rig was drilling an exploratory well . The planned well was to be drilled to 18,360 feet (5,600 m) below sea level, and was to be plugged and suspended for subsequent completion as a subsea producer . Production casing was being run and cemented at the time of the accident . Once the cementing was complete, it was due to be tested for integrity and a cement plug set to temporarily abandon the well . </P>

What was the cause of the deepwater horizon oil spill