The companies involved in the Gulf of Mexico rig disaster have lost billions of dollars in market capitalization since the explosion and sinking that sent a massive oil spill toward the Gulf Coast.

BP's market capitalization declined to $157.13 billion Monday from about $189.3 billion on April 20.

The market value for oil services company Halliburton fell to $28.42 billion from about $30.16 billion. Transocean Ltd., which operated the Deepwater Horizon rig, saw market cap decline to $23.45 billion from $29.6 billion.

Cameron International Corp., maker of a fail-safe device on the well intended to prevent spills, dropped to $9.97 billion from $11.23 billion in market value.

BP PLC, which owns a majority interest in the oil well, said it will pay compensation for "legitimate and objectively verifiable" claims for property damage, personal injury and commercial losses.

President Barack Obama and the attorneys general of five Gulf states have asked the company to explain what that means.

On ABC's "Good Morning America," BP CEO Tony Hayward said the company is responsible for the cleanup and the oil but not for the accident.

Halliburton has said it provided a variety of services, including cementing, on the rig. Cementing is a method of capping a well to control pressure from oil and gas beneath the seabed. A number of lawsuits have been filed claiming Halliburton Inc. improperly capped the well. Halliburton has denied that.

Cameron said it has $500 million in liability insurance for legal claims and has been named in several lawsuits. It said it cannot predict if it has liability for the accident.

Anadarko Petroleum Corp., which has a 25 percent non-operating interest in the rig, watched its valuation decline to $31.54 billion from $36.4 billion.

Shares of BP closed down $1.96, or 3.8 percent, to $50.19 after falling to $47.35 earlier in the day.

Halliburton shares rose 74 cents, or 2.4 percent, to close at $31.39; Cameron closed up $1.31, or 3.3 percent, at $40.77, and Transocean rose 59 cents to close at $72.91.

Anadarko shares rose $1.87 cents to close at $64.03.