US President Barack Obama has said the oil disaster in the Gulf of Mexico will have the same impact on the US psyche as 9/11.
The disaster will "shape how we think about the environment... for years to come", he told US website Politico.
Mr Obama has arrived in Mississippi on his fourth visit to the affected area. He will also visit Alabama and Florida.
Directors of oil firm BP are meeting to decide whether to suspend dividends as company shares have taken a tumble.
BP saw its shares fall by some 9% in afternoon trading in London.
Earlier, BP said the cost of cleaning up the oil spillage had risen to $1.6bn (£1bn).
BP placed a containment cap on its damaged oil well earlier this month; by last week, it was collecting about 15,000 barrels of oil a day.
It is estimated that some 40,000 barrels (1.7 million gallons) of oil a day might have been gushing out before the well was capped.
On Tuesday, Mr Obama will address the US about the oil spill from the White House in a prime-time televised speech.
A presidential aide said he would outline the next steps his administration would be taking over the spill.
Mr Obama had previously visited Louisiana on three occasions. In his Monday visit, he is going to the other states affected by the crisis - Alabama, Mississippi and Florida.
The right lessons
Mr Obama said the disaster would have a lasting impact on US environmental policy.
"In the same way that our view of our vulnerabilities and our foreign policy was shaped profoundly by 9/11, I think this disaster is going to shape how we think about the environment and energy for many years to come," he said in the Politico interview.
Mr Obama vowed to "move forward in a bold way in a direction that finally gives us the kind of future-oriented… visionary energy policy that we so vitally need and has been absent for so long".
"One of the biggest leadership challenges for me going forward is going to be to make sure that we draw the right lessons from this disaster," he said.
Mr Obama said he could not predict whether the nation would make a complete transition from an oil-based economy within his lifetime, but added that "now is the time for us to start making that transition and investing in a new way of doing business when it comes to energy".
"I have no idea what new energy sources are going to be available, what technologies might drive down the price of renewable energies," he said.
"What we can predict is that the availability of fossil fuel is going to be diminishing; that it's going to get more expensive to recover; that there are going to be environmental costs that our children… our grandchildren and our great-grandchildren are going to have to bear."