BP Chief Executive Tony Hayward admitted Monday that he had underestimated the possible environmental impact of the massive oil spill in the Gulf of Mexico.

After inspecting oil-soaked Fourchon Beach earlier in the day, Hayward told journalists that he was "devastated" by what he was seeing at Fourchon Beach, one of the few sandy beaches in Louisiana whose vast marchland is now threatened by the oil spill.

Hayward, who had said in an earlier interview with British media that the environmental impact of the spill would likely be "very, very modest," now admitted that the shoreline had not been very well defended in this unprecedented accident.

"As I said, it's clear that the defense of the shoreline, at this point, has not been successful," he said, adding the spill now is "clearly a major reputational issue for BP."

"We are going to do everything in our power to prevent any more oil from coming ashore and we will clean every last drop up and we will remediate all of the environmental damage," he declared.

In an attempt to restore its spoiled reputation, BP on Monday pledged up to 500 million U.S. dollars to study the environmental impact of the oil spill.

The energy giant agreed to fund the 10-year research program following discussions with the U.S. government and scientists.

U.S. congressman Edward J. Markey last week sent a letter to the company asking for funding.

The program will study the effects of the oil and chemical dispersants used to break up oil on the seabed and the shoreline. It will also study the impact of the dispersant on the oil and ways to improve technology to detect and clean up the oil spill.

The company has been under increasing pressure to stop the month-long oil leak in the Gulf of Mexico. After several failed attempts, it was now pinning its hope on a maneuver called "top kill", a process of using heavy mud and cement to plug the leak.

BP had planned to launch the new method starting on Tuesday, but Doug Suttles, its chief operating officer, said Monday it will be at least Wednesday before the company tries using "top kill" to stop the leak.

"We want this as much as anyone and our best chance of success is looking like Wednesday morning," said company spokesman John Curry, adding the implementation of "top kill" is delayed because more time is needed to get equipment in place and test it.

The spill has so far cost BP about 760 million dollars, including containment efforts, drilling relief wells to stop the leak, grants to Gulf states for their response costs, and payment of damage claims, according to a BP announcement Monday.

At least 6 million gallons of crude oil have now gushed into the Gulf of Mexico since the explosion and sinking of the Deepwater Horizon rig, which was leased by BP, in late April, according to a Coast Guard and BP estimate.

But some scientists believe the spill has already surpassed the 10.8 million gallons of oil spilled off Alaska during the 1989 Exxon Valdez oil spill, the largest oil spill to date in U.S. waters.

Also on Monday a group of about 100 protestors gathered in front of BP's Houston headquarters to voice their anger and concern. The protestors, most of whom claimed to be from the group "Code Pink," were mostly woman dressed in costumes like seagulls and oil-stained fish. Some women went topless, symbolic of what they call the "naked truth" about oil companies.

The protestors mourned the death of the 11 workers and environmental devastation along the Gulf Coast. They also urged BP to be held accountable for an end to offshore drilling and for a restructuring of U.S. energy towards renewable sources.