The US government is putting pressure on BP to clean up the "massive environmental mess" in the Gulf of Mexico amid growing anger at the oil giant's failure, to contain the five-week-old spill.

A delegation of US senators has surveyed affected areas, from the air, and held a press conference, to emphasize, that the cleanup is BP's responsibility. London-based BP, said it would make another attempt to plug the leak on Wednesday, but it may only have a 60-70 percent chance of success.

The company has now lost about a quarter of its market value, that's about 50 billion US dollars, since the spill began. The company, insists it's doing all it can, to try to seal the blown-out well, spewing hundreds of thousands of liters of oil into the Gulf every day. The disaster, threatens to become the worst oil spill in US history.