Warning that "ultimate success is uncertain," BP said Friday it could take all weekend to complete its "top kill" technique aimed at plugging the catastrophic leak in the Gulf of Mexico.
The oil giant issued the statement in Houston hours ahead of President Barack Obama's visit to the oil-stricken region.
The president traveled to Port Fourchon, La., and picked up a tar ball off the white-sand beach.
"You've got about seven miles here where boom has been laid," Obama said, according to a White House pool report that described the president motioning toward what looked like a line of cheerleader pompons strung together.
The president traveled from a Memorial Day weekend stay in Chicago and got the personal tour from Coast Guard Adm. Thad Allen, the federal incident response commander, who showed him the protective boom measures.
The president's motorcade took him past a hand-painted plywood sign declaring "Beach closed" and beachfront cottages on pilings, many with their hurricane shutters closed.
He also was to visit the Coast Guard Station in Grand Isle for visits with the governors of Alabama, Florida and Louisiana -- states whose coastal tourism and fishing industry could be harmed by the Deepwater Horizon disaster.
The president's trip was his second to the gulf region since the April 20 oil rig accident triggered the worst spill in U.S history.
Thursday, he cautioned that there were no guarantees of success for the top kill technique in a White House news conference early entirely devoted to the matter in which he said, "I take responsibility" for its handling.
BP was guarded in its morning statement, which reported: "Operations on the top kill procedure continue. . . It is estimated that the full top kill procedure could extend for another 24 to 48 hours. If the well were successfully 'killed,' it is expected that cementing operations would then follow."
The top kill procedure has never before been attempted at these depths. BP noted that should the top kill technique fail, engineers were preparing an alternative plan.
In Washington, Interior Secretary Ken Salazar named Bureau of Land Management Director Bob Abbey acting director of the Minerals Management Service.
The Obama administration's director of 11 months resigned this week amid unrelenting criticism of the federal government's lax oversight of BP and the rest of the offshore oil industry.