Four Filipinos, an Austrian, a Bangladeshi, a Czech and a Ghanaian were taken with an unidentified ninth foreigner, Austrian officials say.
The foreign ministry in Vienna said ISIS had attacked the al-Ghani oil field.
The al-Ghani oil field, 440 miles south-east of Tripoli, had been attacked on March 6.
The foreigners were working for oilfield management company Value Added Oilfield Services (VAOS) at the field.
VAOS said it did not know which militants had carried out the attack or where the oil workers had been taken.
It insisted that none of its employees had “died or were physically harmed in the attack”.
Confirming that four of the missing workers were their nationals, the Philippines said it brought to seven the number of Filipinos now missing in Libya.
Last week, ISIS militants were reported to be behind an attack on two oil fields in Bahi and Mabruk.
Rival militias have been fighting for control in Libya since Muammar Gaddafi was ousted in 2011.
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