Spain's Compania Espanola de Petroleos SA said it moved workers from two Algerian facilities to the centre of the country as a precautionary measure and that its Algeria operations were functioning normally. Spain gets nearly half its natural gas from Algeria.
BP PLC said plans are under way to bring some non-essential workers out of Algeria.
Helge Lund, the CEO of Norwegian energy company Statoil, said about 40 non-essential staff would be flown back to Norway.
The hostages were taken Wednesday by militants linked to Mali's rebel Islamists at a remote Sahara natural gas plant. The site is operated by BP, Statoil and the Algerian state oil company Sonatrach. A Japanese company, JGC Corp, provides services for the facility.