After a rapidly freezing mix of natural gas and water derailed attempts to place a big underwater dome on top of a deepwater well leaking oil into the Gulf of Mexico, BP hopes a smaller dome will do the trick, Chief Executive Tony Hayward said Monday.

The big dome failed because "there's a lot more gas involved in the leak than we had hitherto believed" that combined with water to form hydrates that clogged a 12-inch opening at the top of the structure, said Hayward. The new steel dome-- five feet in diameter, five feet tall and shaped like a "top hat"-- will be ready to deploy within 72 hours, the executive said in a meeting with reporters at BP's Houston campus.

The company will pump methanol into the new dome to keep ice from forming, he said. Also, the smaller size of the structure should keep water out.

Hayward's comments came after several attempts to shut off the 5,000 barrel-a-day spill -- ranging from the giant subsea dome to shutting off a giant underwater blow-out preventer using robots -- have failed.

But BP is still trying to fight the spill on the surface, at the shoreline and at the well site, the CEO said. Concurrently with the small dome, BP is drilling a relief well to kill the leaking well, an effort that is expected to take months. A second, back-up relief well will be drilled starting at the end of the week, "probably Friday," he said.

"The relief wells will ultimately be successful," Hayward said. He added that the company will solve the problem -- "it's simply a question of how long it takes."

The spill resulted from the explosion and sinking in April of the Transocean Ltd., Deepwater Horizon drilling rig, which was finishing a well for the London-based oil giant. Eleven members of the crew were killed by the blast, and the spill threatens the shore of several Gulf Coast states. It also risks undermining U.S. appetite for offshore drilling. Much of the difficulty in containing the leak is its depth.

Hayward called the incident "unprecedented in over 20 years of deepwater exploration," and said the lessons learned here "will have profound implications for the industry."

BP, which is responsible for the leak, is also planning a "junk shot" of diverse materials in an attempt to block off the blow-out preventer. The shot would contain tire pieces, knots of rope and other items, and will be tried in the next two weeks, said Kent Wells, a senior exploration executive for BP.

The company resumed injecting dispersant at the source of the leak on Monday, Hayward said, a process that concerned environmentalists and federal authorities due to the toxic nature of the chemicals involved.

But its use "seems to be having a very significant impact" in dispersing the leak, and is being carefully monitored, he said.

BP has been "successfully containing [the spill] to a large degree," according to Hayward, as most oil is restricted to the "vicinity of the well."