A summary of May 12 events related to the vast oil spill from the Deepwater Horizon

Events May 12, Day 23 of a Gulf of Mexico oil spill that began with an explosion and fire on April 20 on the drilling rig Deepwater Horizon, owned by Transocean Ltd. and leased by BP PLC, which is in charge of cleanup and containment. The blast killed 11 workers. Since then, oil has been pouring into the Gulf from a blown-out undersea well at about 210,000 gallons per day.


Rep. Henry Waxman said his committee's investigation into the Gulf oil spill revealed that a key safety device, the blowout preventer, had a leak in a crucial hydraulic system. The California Democrat said in a second day of hearings into the spill that the investigation also discovered that the well had failed a negative pressure test just hours before the April 20 explosion.


BP PLC announced Wednesday that a new containment box — a cylinder called a "top hat" — was on the sea floor near the wild well that has spewed at least 4 million gallons into the Gulf of Mexico. Engineers hope to work out ways to avoid the problem that scuttled an earlier effort with a much bigger box before they move the cylinder over the end of the 5,000-foot-long pipe from the well. The 100-ton box filled up with an ice-like slush of gas and water, lifting it up and clogging its nozzle.


The White House has asked Congress to raise a liability cap that could limit how much BP has to pay in economic damages. The administration also wants to increase a per-barrel tax on oil companies to replenish a cleanup fund. President Barack Obama also sent a proposal to bring more unemployment assistance and food stamps to help fishermen along the Gulf Coast.


A Minerals Management Service official said a blitz inspection of deepwater drilling rigs turned up only "a couple of minor issues." At a hearing led by the MMS and the Coast Guard in Kenner, La., a Coast Guard official questioned whether the government had an effective safety net for the manufacturing and installation of blowout preventers. Michael Saucier of the MMS testified the government isn't required to inspect the safety devices before they are installed.


In the weeks after an oil rig exploded and killed 11 men in the Gulf of Mexico, worried environmental groups scoured the water for oil plumes, set up animal triage centers and stretched boom across shorelines. Activists hope their involvement doesn't end there. They contend this may be the catalyst that America's green movement needs to get Americans to pump less gasoline, buy hybrids and downsize their consumer lifestyle.


The explosion of the Deepwater Horizon oil rig illustrates the energy industry's push to drill ever deeper in search of huge oil deposits, despite the mammoth risks and unique challenges associated with exploration in such a hostile environment. The lure of the deep is driven by technological advances that make previously inaccessible oil now reachable, and dwindling supplies at shallower depths due to years of exploration. High energy prices and lucrative government incentives have also made it more financially feasible.


Federal wildlife officials are treating the deaths of six dolphins on the Gulf Coast as oil-related even though other factors may be to blame. Blair Mase of the National Marine Fisheries Service said Tuesday that the carcasses have all been found in Louisiana, Mississippi and Alabama since May 2. Samples have been sent for testing to see whether oil contributed to the deaths.