The cap on the damaged well in the Gulf of Mexico is keeping up to 1.7 million litres of oil a day from leaking, the U.S. government says.
Coast guard Admiral Thad Allen, the man in charge of the U.S. government's response to the oil leak crisis, says crews are hoping to increase the amount being collected.
He said BP is planning to move another ship into the area.
Allen told reporters at the White House that authorities are dealing with "hundreds of thousands" of individual oil spills in the Gulf now.
He said smaller vessels will have to be recruited to clean up the numerous oil patches using skimmers.
Allen warned that the battle to contain the oil will probably continue into the fall. The cap installed last week is not containing all the oil.
"You know, when the relief well is finished and it's capped, sometime in August, oil will have flowed to the surface in some manner because we probably won't get 100 percent containment, we want as much as we can get, so there'll still be oil on the surface the day the well is capped," he said.
He added it could take years for environment to be restored following the spill.
"Dealing with the oil spill on the surface is going to go on for a couple of months," he said. "Long-term issues of restoring the environment and the habitats . . . will be years."
Officials have expressed worry that a stronger than normal hurricane season this year could wreak havoc with cleanup efforts.
"There may be times when we're going to have to disconnect that operation and re-establish it," Allen said.
"This is a long campaign and we're going to be dealing with this oil for the foreseeable future."
With files from the Associated Press
