"There will need to be reassessment," said McCredie, now CEO of Forbes Research Group in the United States.

Nigel Inkster, a former senior British intelligence officer who heads a risk-analysis unit at the International Institute for Strategic Studies in London, said the incident raised questions both for oil companies and Algeria.

"The boardrooms of oil companies looking to work in Algeria are going to be convulsed by this, and uncertain of how to proceed," Inkster said. "It raises all sorts of concerns about all sorts of economic activity ... (including) uranium mines in Niger, which are pretty important to the global economy."

Algeria has taken a strong tack against the terrorists, rejecting offers of help from Britain, the U.S. and other to go it alone in a typical tough and uncompromising response. BP and Statoil were compelled to entrust their employees lives to the Algerian security forces, and that won't change â¿¿ at least immediately. Algeria insists that it has the know-how to assure the security of energy plants.

"We are going to reinforce the security and we will rely first of all on our own means," Algerian Energy Minister Youcef Yousfi said on Sunday, according to state news agency APS. "There is no question of accepting outside security forces."

BP and Royal Dutch Shell, whose employees in Nigeria have been the targets of gangs of kidnappers and militants, would not comment on security arrangements in Algeria. But Ted Jones, the CEO of specialist evacuation company Northcott Global Solutions in London, noted companies alarmed by the attack are scaling up their physical security, moving from unarmed to armed operations, and shifting nonessential staff to safer locations.

Companies can become complacent after a period of safe operation, he said, then change course when something terrible occurs.

"Suddenly something like this happens and they realize they're much closer to the danger ... and there's a sort of panic response, which is perfectly natural," he said.

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