Gunmen kidnapped the four foreigners and two Nigerians working on Hyundai’s operations in the Niger Delta region on Monday.
Officials in Seoul said in a statement that the four Koreans had been freed, but gave no details of the fate of the Nigerian workers.
South Korea’s Foreign Ministry said the four workers were released after “persistent persuasion.”
The four hostages had been handed over to South Korean officials in Nigeria late on Friday, Yonhap news agency and YTN TV said.
There was no immediate comment from either the South Korean government or Hyundai Heavy Industries.