By Cosmic Log

Illustration by AP Click for interactive: Drilling mud is being pumped into equipment at the bottom of the Gulf of Mexico in hopes of cutting off the flow of oil. Click on the image to explore an interactive graphic.

Never have so many hopes rested on so much mud: The "top kill" maneuver that got under way today is the latest best strategy for cutting off the catastrophic Gulf of Mexico oil spill. And the key to the top kill is millions of gallons of a viscous fluid known as drilling mud. This mud is not your garden-variety sludge: It's an industrial-strength blend of water and minerals, generally including an absorbent, slippery kind of clay known as bentonite. Drilling fluid is used for a wide variety of purposes in oil fields - as lubricants, coolants, drill cleaners or hole fillers. That last application is how it's being used in the Gulf: As shown in this interactive graphic, gallons of heavy, gloppy drilling mud are being pumped into the half-broken blowout preventer on top of the wellhead. The idea is that the dense fluid will eventually press down on the oil rising from thousands of feet below and clog up the oil line. This posting on the Oil Drum forum compares it to trying to get your basement drain to back up. Another way to think of it is like ketchup that has a hard time blurping out of the bottle. The BP oil company, which is still responsible for cleaning up the Gulf mess, has laid in 50,000 barrels (2 million gallons) of drilling mud for the job. The pumping operation began this afternoon, and as of this evening's news conference, BP chief operating officer Doug Suttles said more than 7,000 barrels had been pumped in. "The job has been proceeding as planned," Suttles said. BP executives have estimated that this latest strategy has a 60 to 70 percent chance of working. The problem is that the mud has to fill the blowout preventer and sink down into the well, counteracting the pressure of spurting oil. That pressure might be so great that the mud is pushed out of the leaking pipes as fast as it can be pumped in. There's even a chance that the drilling mud will ream out the contraption's partially closed valves, opening the lines to create an even bigger oil gusher at the bottom of the sea. In the aftermath of the Persian Gulf War, oil wranglers like the late Red Adair used the top-kill strategy to stop up sabotaged oil wells in Kuwait - but doing it using robo-submarines a mile beneath the ocean surface is something completely different. Will Red Adair's successors pull this one off? If this doesn't work, you can forget the top kill and start thinking about the next strategy, known as the lower marine riser package or LMRP Cap Option. That involves cutting off the top of the blowout preventer and putting a cap on top to suck up the oil. This slide presentation provides a graphic look at BP's next steps, and this BP video provides a technical overview. More about oil-spill strategies:

Update for 12:50 a.m. ET May 31: The top-kill effort didn't work, and BP is moving on to the LMRP Cap Option. Join the Cosmic Log corps by signing up as my Facebook friend or hooking up on Twitter. And if you really want to be friendly, ask me about "The Case for Pluto."

Cosmic Log