Question: what was the cause of the deepwater horizon oil spill
Answer: 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 .