The oil company BP is to decide on whether to carry out a new plan to try to stem the leaking Gulf of Mexico oil well, the chief executive has said.
Tony Hayward said the procedure would begin on Wednesday if considered safe.
Teams have been carrying out diagnostic tests to ensure the "top kill" method is feasible and will not backfire. The government has approved the measure.
Meanwhile, a congressional memo has revealed there were several warning signs shortly before the rig exploded.
According to the document, BP officials told congressional investigators on Tuesday that a decision to continue drilling after unusual pressure readings may have been a "fundamental mistake".
BP said the buildup of pressure was an "indicator of a very large abnormality" in the well, the memo by representatives Henry Waxman and Bart Stupak said.
Problems were also identified with equipment including the blowout preventer - meant to shut down the well in the case of emergency - and potential gas leakage in the hours prior to the 20 April explosion, the memo said.
Speaking on US television on Wednesday, Mr Hayward said: "What we're seeing here is a whole series of failures. We've identified... at least seven.
"It's very clear that much more needs to be put in place to deal with this situation should it ever occur again."
He added: "It's clear that this will be a transforming event in the history of deep water exploration."
Questions were raised in the memo as to whether proper procedures were followed in carrying out pressure testing and other activities in the 24 hours before the explosion.
A worker for Transocean, the Deepwater Horizon rig's owner, told US Coast Guard investigators he had heard senior managers complaining that BP was "taking shortcuts" by using seawater instead of drilling mud in the well before the blowout, according to witness statements seen by the Associated Press news agency.
BP is under intense pressure to succeed with its latest attempt to stem the leak, after previous measures failed.
"I have to say that it will be a day or two before we can have certainty that it's worked," Mr Hayward told the US network NBC's Today show.
Coast Guard Adm Mary Landry said federal authorities had approved the "top kill" measure - the final authorisation needed for BP to decide whether to go ahead.
Speaking on a visit to California, President Barack Obama said: "If it's successful, and there's no guarantee, it should greatly reduce or eliminate the flow of oil now streaming into the Gulf from the sea floor."
He said the "heartbreaking" spill highlighted the need to find alternative energy sources.
"We will not rest until this well is shut, the environment is repaired and the clean-up is complete," he added.
If the new procedure is used, heavy drilling fluids - such as mud - will be injected into the well about a mile (1.5km) underwater.
Engineers hope to follow this with cement, designed to seal the well.
The company has said it estimates a 60-70% chance of success.
Officials say the method has been used before in other areas of the world, but not at the depths required to stem the oil from the Deepwater rig.
If the operation goes ahead, it can be watched via a live video stream of the site, which currently shows plumes of oil and gas escaping from the well.
A conservative estimate of the amount of oil escaping is about 5,000 barrels (210,000 gallons, 795,000 litres) a day, while some scientists say it could be many times greater.
The US government has declared a "fishery disaster" in the seafood-producing states of Louisiana, Mississippi and Alabama.
A massive containment and clean-up operation is under way, as the oil reaches the beaches and vulnerable marshlands of a 150-mile stretch of coast.
Some workers involved in the operation are complaining of health problems after contact with oil and chemical dispersants, the Los Angeles Times reports.
The fishermen, who say they are suffering from nausea, dizziness and breathing problems, told the paper they were not issued with special equipment but were simply told by BP not to pick up oil waste.
Louisiana Congressman Charlie Melancon has urged the federal government to set up mobile clinics in rural area to treat those affected, the paper reports. BP has said conditions are being monitored.
'Plug the hole'
Mr Obama is due to make his second visit to the Gulf of Mexico region on Friday.
His visit will come a day after he receives a report into offshore drilling that is expected to recommend tougher regulations and demand more safeguards.
In the tests which began on Tuesday, five spots on the well's crippled five-story blowout preventer were being checked to make sure it could withstand the heavy force of the injection.
A weak spot in the device could blow under the pressure, causing a brand new leak at the site 50 miles (80km) off the Louisiana coast.