In a statement Saturday, BP said that of 18 BP employees working at the plant in the Sahara, 14 are now safe, two with non-life-threatening injuries.
"We have great fears we have likely suffered one or more fatalities," said BP CEO Bob Dudley. For the victims' families, said Dudley, "this is a terrible and agonizing ordeal."
The status of four employees, however, remains unknown. The facility is a joint venture with the Norwegian company Statoil and the Algerian national oil company
The al Qaeda-linked group claims the attack on the facility in the middle of the Sahara desert had been planned for some two months.
In both assaults, the Algerian Army, using tanks and helicopters, found the terrorists were heavily armed and prepared to fight to the death.
One official described the aftermath as carnage.
Hostages who escaped or were freed said the terrorists only wanted Westerners or Americans, and were brutal in their treatment of some of them.
A Scottish worker named Ian said he had "never been so relieved as when they came and got us off site."
Ian said he was "very, very relieved to be out. Obviously, we still don't know what's happening back on site. As much as we're glad to be out, our thoughts are with colleagues still there at the moment."
Another worker, Stephen McFaul of Ireland, said he escaped as the terrorists tried to drive them to another location and the Algerian army opened fire on the convoy.
American officials had urged the Algerians to go slow, out of concern for the safety of the hostages, but that advice was ignored.
"They didn't let the terrorists dig in," said Richard Clarke, a former White House counterterror advisor and now an ABC News consultant. "They didn't negotiate. They moved quickly."
The attack has led the U.S. and its allies to marshal resources to track down the alleged mastermind, Mokhtar Belmokhtar, who operates from a safe haven in the northern part of the country of Mali, a thousand miles away.
French military aircraft were already taking action against Belmokhtar even before the Algerian attack, according to ABC News correspondent Bazi Kanani, who is in Mali's capital, Bamako.
In southern Mali, according to Kanani, "there's limited information coming down from the north where journalists aren't allowed to go, but we do know one of the first targets of the French war planes that arrived one week ago was the headquarters of the leader of the terror group involved in the Algerian hostage crisis. "
U.S. officials say they won't send troops to Mali, but they are sharing intelligence with France, and by Monday, the U.S. Air Force will be helping to fly French troops and equipment here.
U.S. officials say they will work with the French and others to make sure Belmokhtar pays a price.
"Those who would wantonly attack our country and our people will have no place to hide," said Secretary of Defense Leon Panetta.