GuLF Study Environmental Health Sciences (NIEHS), part of the National Institutes of Health, and aims to recruit 55,000 of the 150,000 workers who volunteered or were employed to help clean up the spill. It is led by Dale Sandler, head of the NIEHS's epidemiology branch. The "Deepwater Horizon" oil spill was the world's largest accidental marine oil spill. It began on 20 April 2010 after an explosion on the "Deepwater Horizon", a drilling rig leased by BP to drill an exploratory well. Between then and 15 July, when the well was capped, over four million barrels of oil (around 170 million US
Montara oil spill 1 November. The West Triton jackup drilling rig arrived at the Montara Field in an attempt to plug the oil leak on 11 September 2009. Oil and gas producer, Woodside Petroleum Ltd offered to assist PTTEPAA in cleaning up the oil spill with the use of a rig closer to the spill site. However, PTTEPAA rejected the Woodside offer on the basis of "safety reasons". The Woodside rig was a semisubmersible drilling rig and, as it floats on the sea surface, was not deemed as a suitable platform for the relief well. A jackup rig was required because it could