The three were seized on board the MV San Miguel on January 3 and taken to the Bonny Channel area of the oil-producing Rivers state, in southern Nigeria.
The Department of State Services (DSS) yesterday said they were rescued in a joint operation with Nigeria's military on Thursday.
"On January 31, the three Indians were handed over to the Indian High Commission and the country of their employers (Equatorial Guinea Embassy) respectively," said DSS spokeswoman Marilyn Ogar.
Five of the suspected kidnappers have been arrested but the hunt was still on for the ringleader and other members of the gang, Ogar added.
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News of the kidnapping came after a Greek-owned oil tanker, the Kerala, disappeared off Angola in a suspected piracy attack earlier this month.
Kidnappings of oil workers have been commonplace in the Niger Delta region by armed indigenous groups demanding a greater share of revenue from production.
Seizing crew from ships in the Gulf of Guinea has usually been linked to the theft of cargo from vessels.
Piracy off the Horn of Africa was down more than 90 per cent from its peak in 2011 but an increase off the coast of west Africa was a cause for concern.
West African piracy made up 19 per cent of attacks worldwide last year. Nigerian pirates accounted for 31 of the region's 51 attacks -- the most since 2008.