The work involved in shutting down the nearly 200,000 gallons of crude oil spewing up into the Gulf of Mexico daily for the past two weeks has demanded a tremendous amount of coordination involving, among others, BP, the U.S. Coast Guard and local fishermen. But given the depth of the damaged Macondo well—1,524 meters below the Gulf's surface—the use of undersea robots is the only way to cut off the flow of escaping oil.

Specifically, the robots are remotely operated vehicles (ROVs), and they are playing a major role in efforts to stop each of the three leaks created following an April 20 explosion on board the drilling rig Deepwater Horizon, which killed 11 workers, sunk the rig and damaged the pipeline. (The cause of the explosion remains unknown.)

ROVs are a general-purpose work tool used by drilling companies, "the pickup trucks that deliver tools down to drilling site and specialize in the physical manipulation of objects," says Glenn Sasagawa, development engineer at the Scripps Institution of Oceanography's Institute of Geophysics and Planetary Physics. Most of these rigs begin drilling too deep for human divers, so the companies use million-dollar ROVs, ranging from 10 to 300 horsepower, for inspection, maintenance and intervention.

Crews capped one of the leaks Tuesday night with the help of robotic subs controlled remotely from a ship on the surface. The ROVs installed a specially designed valve over the end of a leaking drill pipe lying on the sea floor, The New York Times reported Wednesday. The end of the pipe was cut, after which the valve, weighing more than half a ton, was positioned on the seabed, Offshore-mag.com reported Wednesday. The ROVs secured the valve to the broken drill pipe and then closed it, shutting off flow from the pipe.

ROVs have been less successful in capping the leak at the well itself—specifically, by activating the blowout preventer. The Macondo well's blowout preventer is a 12-meter-tall steel structure containing several valves, and it is designed to plug the well in an emergency. The rig's crew was unable to activate the blowout preventer from the rig before it sank. The robots have been unable to reach all of the valves to shut them off, and the ones that the subs have been able to close are leaking.

A third effort underway involves placing a four-story, 100-ton concrete-and-steel containment box on the ocean floor over the largest leak, where 85 percent of the oil is escaping. Workers began lowering the device to the seabed Thursday, but it will likely be Sunday or Monday before it is fully operational.

Crews are positioning the box with the help of ROVs, which are placing buoys around the main oil leak to act as markers to help line up the box as it descends, the Associated Press reported Friday. The underwater robots are also clearing pieces of pipe and other debris from the site where the box will sit. Once in place, a steel pipe will then be attached to a tanker at the surface and connected to the top of the box to move the oil. If the box can contain the bigger leak, a second box being built may be used to stop the smaller leak at the blowout preventer.

As water depths for drilling have increased, engineers have designed the blowout preventers, subsea valve arrangements and other equipment to be handled by ROVs, says Craig Dawe, technical support and operations manager for Monterey Bay Aquarium Research Institute's Monterey Accelerated Research System in Moss Landing, Calif. "The design is such that the ROV can operate and install valves and other equipment by use of specially built tools or with the ROV manipulators," he explains.

As oil rigs move into ever deeper waters, however, engineers will increasingly depend on subs that can operate autonomously, says Andy Bowen, a research specialist in applied ocean physics and engineering at the Woods Hole Oceanographic Institution in Woods Hole, Mass. Humans will act more as supervisors of the work these autonomous underwater vehicles (AUVs) do, rather than directly controlling thrusters, arms and other equipment on the sub.

Operators can communicate with AUVs in several different ways, including low-frequency acoustics for long distances and high-frequency coded acoustics for medium distances, Bowen says. "The robot has to be smart enough to shift elegantly between these different communications modes, each one requiring a different degree of autonomy," he adds.

Bowen envisions a time when operators place one or more autonomous vehicles on the ocean bottom for extended periods of time. This would lead to faster response times when problems arise because the AUVs would act on the basis of their preprogramming before people on board a ship can get to the site, he says. "If [there had been] a vehicle on the sea floor that was providing an intervention capability, it's quite possible that it could have played some meaningful role in how things unfolded with the Deepwater Horizon," he adds.