The contract workers were ambushed while ferrying supplies by barge to Shell's Forcados/Yokri oil and gas facility in the Niger delta on Sunday. Security forces freed some of the hostages, but nine had remained captive.
The hostages were seized at Abrabebe community, near the oil city of Warri, said Shell spokesman Simon Buerk in London.
"Following intervention of elders and leaders of the Ogulagha community, all nine crew members have been released," he said.
A military spokesman in Warri said 15 military personnel who were escorting the barge were being interrogated for allegedly conniving with the militants.
The attack came after similar ambushes on contractors to ChevronTexaco elsewhere in the Niger delta, where local communities accuse oil majors of giving them little except pollution for the riches pumped out of their land.
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