Via MSNBC:

BP said Wednesday it had begun injecting mud into the blown-out well in the hopes of stopping the Gulf oil disaster, shortly after the Coast Guard gave it a green light and its chief executive issued an apology of sorts.

The oil giant said the operation started at 2 p.m. ET.

Earlier, CEO Tony Hayward said it would take a day or two to see if the risky procedure worked.

Meanwhile, it seems BP's ass-covering story about how the spill occurred is falling apart:

As BP readied another attempt to slow oil gushing into the Gulf of Mexico, two congressmen said Tuesday that the company's internal investigation into the spill has identified new warning signs of problems before the April 20 explosion that brought down the Deepwater Horizon rig.

Reps. Henry Waxman and Bart Stupak said in a committee memo that the warning signs include an unexpected loss of fluid from a pipe known as a "riser" five hours before the explosion. That suggests there could have been a leak in the blowout preventer.

Engineers conducting tests on the system reduced the pressure to one of the lines to zero, while the pressure on the drill began to build. The memo says BP's investigator indicates that may have been a "fundamental mistake" because the rising pressure was an "indicator of a very large abnormality."