BP boss Bob Dudley on Tuesday warned that he "feared the worst" for four of its staff members still unaccounted for following the bloody In Amenas hostage crisis in Algeria.
"We have been gravely concerned for these colleagues and feared one or more fatalities among their number," he said.
"It is with great sadness that I now have to say that we fear the worst for them all. We are doing all we can to support their families and ask everyone to show them consideration and to respect their privacy."
Signup to our newsletter and follow us on Facebook and Twitter!
The oil giant will hold a minute's silence at offices around the world on Wednesday in respect to those who lost their lives at the gas field.
Algerian authorities searched on Tuesday for five foreigners still missing and tried to identify seven charred bodies, days after the crisis ended, a security source said.
"Still no news about the five missing foreigners," the source told AFP, after Algerian special forces launched a final assault on Saturday against Islamist gunmen at the remote desert gas plant, where the attackers seized hundreds of hostages.
Thirty-seven foreigners of eight different nationalities and an Algerian were killed during the siege by the hostage-takers, who were demanding the release of Islamist prisoners and an end to France's military intervention to wrest back control of northern Mali from armed Islamist groups.