"A group of armed men came to the compound and killed staff" late yesterday, a senior official at the Greater Nile Petroleum Operating Company (GNPOC) said, not wanting to give his name as he was not authorised to speak to the media.
It was not clear if the attack was linked to rebel battles with government troops following an alleged coup attempt against South Sudan President Salva Kiir.
However, attacks by militia forces and clashes between heavily armed cattle herders are common in the region, the home state of the fugitive former vice president Riek Machar, who is accused by Kiir of launching the coup bid.
The United Nations peacekeeping mission said it was sheltering civilians in Bentiu, the main town of Unity state.
In a separate attack, 11 people were reportedly killed in the Thar Jath oil field, also in Unity state.
