What happened: A massive explosion on the Deepwater Horizon oil rig killed 11 workers and caused an uncontrollable fire on April 20, destroying the $500-million (U.S.) station. In less than two days, the rig had sunk beneath the surface of the Gulf of Mexico, just 80 kilometres off the Louisiana coast, which is home to a variety of wildlife and seabird reserves as well as the fish and shrimp that help feed the region.
The rig was being leased from the Swiss company Transocean by BP Exploration and Production, which initially said the environmental impact from the disaster would be manageable. But on Saturday, a leak near the ocean bed was discovered to be releasing more than 160,000 litres (42,000 gallons) of oil every day - the equivalent of about five large tanker trucks full.
BP is now working with the United States Coast Guard, U.S. Minerals Management Service, Louisiana Department of Environmental Quality, National Oceanic and Atmospheric Administration, U.S. Fish and Wildlife Service, Louisiana Wildlife and Fisheries, and the Marine Spill Response Corp. to try to contain and clean up the spill.
What happens next: The rig had been drilling for crude oil in a reservoir in the Rigel gas field about 1,500 metres beneath the seabed. When the rig sank, its pipeline to the reservoir crumpled, and the major leak is coming from the first fold in the pipe, with a secondary leak located about two metres from the wellhead, at the seabed.
The U.S. Coast Guard has sent robot submarines to try to stop the leaks by activating the blowout preventer, a series of pipes and valves at the wellhead designed to automatically clamp shut over the base of the leaking well pipe. It failed during the explosion, which is believed to have been triggered by the uncontrolled escape of gas from the well.
The submarines are equipped with cameras and remote-controlled arms to activate the blowout valves manually. The work will be done 1.5 kilometres below the ocean surface and was expected to take 24 to 36 hours - if it works. BP's chief operating officer, Doug Suttles, described the plan as a "highly complex task."
If that doesn't work: If they can't turn off the leak, the clean up group plans to cut the oil off at its source. On Monday, a second oil rig, called the Development Driller III, arrived to start drilling a relief well into the oil reservoir beneath the ocean. The relief well would relieve pressure at the leak site, and be used to inject cement to block the flow of oil. The original well will then be permanently sealed. "We are attacking this spill on two fronts - at the wellhead and on the surface offshore," said Tony Hayward, BP's chief executive. The thing is, this option could take several months to complete.
In the meantime: In an office set up in Houma, La., more than 500 people are working to monitor the size and location of the oil that has already been spilled. By Monday morning, the oil slick on the ocean surface measured approximately 1,500 square kilometres. The prevailing weather pattern is helping keep the slick about 80 kilometres off the coast, where it could do untold damage, and waves are helping break up the heavy crude oil, which will eventually harden and sink back to the ocean floor.
BP has deployed 378,541 litres of dispersant to thin the oil and make it easier to skim from the water's surface. There are 32 boats working to contain and collect the oil, as well as five helicopters and airplanes deploying the dispersant. By Sunday, the group had retrieved about 1,052 barrels of oily water.
And at some point: There is also the matter of the rig itself, which is believed to contain about 2.6-million litres (700,000 gallons) of diesel. Mr. Suttles told a news conference that the rig was "intact and secure" on the seabed about 500 metres from the well site.