US President Barack Obama has officially unveiled a commission to investigate the Gulf of Mexico oil disaster.
In his weekly television and internet address, Mr Obama blamed the spill on a breakdown of responsibility at energy giant BP, and other companies linked to the spill - Halliburton and Transocean Ltd.
He said his administration would hold the companies, and Washington, accountable. Offshore oil drilling could only go forward if there were assurances that such accidents would not happen again, Mr Obama said.
Two political veterans, former Democratic Senator Bob Graham and former Republican environment chief William Reilly, are to head the panel.
US lawmakers and scientists have accused BP of trying to conceal what many believe is already the worst US oil spill, eclipsing the 1989 Exxon Valdez accident in Alaska. It represents a potential environmental and economic catastrophe for the US Gulf coast.
A month after the well blowout and rig explosion that killed 11 workers, sheets of heavy oil are starting to clog fragile marshlands on the fringes of the Mississippi Delta, damaging fishing grounds and wildlife.
The spill has raised major questions about Mr Obama's earlier proposal to expand offshore drilling as part of strategy to win Republican support for climate change legislation.