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-- BP's next attempt to stop the oil leak in the Gulf of Mexico will involve a maneuver called "top kill," in which heavy drilling fluid is to be pumped into the head of the leaking well at the seafloor.
The manufactured fluid, known as drilling mud, is normally used as a lubricant and counterweight in drilling operations. The hope is that the drilling mud will stop the flow of oil. If it does, cement would then be pumped in to seal the well, according to BP.
BP said it hopes to start the procedure Wednesday morning. Here, in a question-and-answer format, is a more detailed look at how it would work:
How will the drilling mud be pumped into the well?
Two vessels loaded with a total of 50,000 barrels of drilling mud will feed a rig that will manage the pumping process.

Video: Sealing the leak

The rig will send the drilling mud into a pipe that will go nearly down to the seafloor, 5,000 feet below the surface. The fluid will split off into two flexible hoses that will connect to a manifold, which is a distribution chamber that BP has placed on the seafloor. The manifold's job is, among other things, to manage the flow of mud into the well, according to BP.
The manifold will send the fluid through two other hoses that will be attached to the blowout preventer that sits atop the well. The blowout preventer is a 48-foot-tall valve-like apparatus that should have prevented the leak in the first place, but is not working.
Remote-operated submarines will have attached the hoses to lines in the blowout preventer that access the well.
How will the drilling mud help stop the oil?
If the drilling mud can be pumped into the well at a sufficiently high pressure, it could overcome the pressure of the oil and gas that is trying to come out, thereby stopping the oil flow, according to BP.
"[The drilling mud] is heavier than the oil and the gas. The objective is to put it into the well so it will reduce the pressure and flow from the well," which would then allow BP to pump cement into the well, BP spokesman John Curry said.
BP has cautioned, however, that this procedure hasn't been tried at such a depth. BP CEO Tony Hayward told reporters Monday that the company rates the chance of success at 60 percent to 70 percent.
What will happen if the drilling mud doesn't work?
Using the same tubes and pipes, BP would then try a "junk shot," pumping material like golf balls, pieces of tire and pieces of rope into the blowout preventer.
"Each of these [materials] has been proven to fill various sized spaces in the blowout preventer until the flow is stopped," BP says in a statement on its website. "While there is no known perfect 'recipe,' a number of combinations of materials will be used."
More drilling mud would follow the junk shot, with the hope that the two methods together would stop the oil long enough for cement to be poured into the well.
How long will the attempt take?
Curry said BP doesn't know how long the process will take, but it won't be instantaneous.
"It's a process. We will make sure we take the time to do it right," he said.
A joint website for the government agencies and companies involved in dealing with the leak says the total operation could take several days. It's not clear whether that includes preparation, which already is under way.
What will happen if the "top kill" and "junk shot" procedures don't work?
One option is adding another valve, or an additional blowout preventer, on top of the blowout preventer already on the well, according to BP. That potentially could cut off the oil flow.
BP also may try to sever the ruptured riser that extends from the blowout preventer -- it is this pipe that is leaking -- and fit a containment dome over it, BP Chief Operating Officer Doug Suttles said Monday. From this dome, the oil would be piped up to a ship on the surface, and this would be done until BP can seal the well.
A larger containment dome failed to work earlier this month. BP this month also inserted a tube into the ruptured riser to capture some of the leaking oil. That captured oil is being pumped to a ship on the surface.
Other ideas also are being considered, BP says.
BP says the plan to permanently kill the well, regardless of whether the "top kill" procedure works, involves drilling relief wells that will intersect with the well in question, far below the seafloor. Once contact is made, concrete will be put into the well producing the leak above.
Drilling relief wells takes about 90 days. Drilling for the first one started in early May, and drilling for a second, backup relief well began two weeks later, according to BP.
How is the federal government involved in the attempt?
Federal officials and scientists "have been working with BP engineers on the review of the various operations, procedures and contingencies" that will be used during the "top kill" attempt, according to the joint leak-response website.
On Sunday, U.S. Coast Guard Commandant Adm. Thad Allen told CNN's "State of the Union" that BP "had to go step by step [with government officials] on how they're going to do this 'top kill.' "
"All the assumptions that BP put forward were questioned by people like" John Holdren, the director of the White House's office of science and technology policy, Allen said.