BP said Steve Green, 47, was the fourth victim of the attack on the Ain Amenas gas facility in eastern Algeria last month.
"These men were murdered while carrying out their jobs on a normal working day. It was a calculated and evil act," BP Chief Executive Officer Bob Dudley said in a statement.
The facility is operated by BP, Norwegian energy company Statoil and state-owned Sonatrach. At least 37 employees of the companies died in the attack and the raids that followed. Statoil in early February confirmed five employees died in the attack.
Militants sympathetic to al-Qaida in the Islamic Maghreb stormed the Ain Amenas facility last month.
The attack was said to be a response to an Algerian decision to let French forces use their airspace for a multilateral intervention in Mali, where al-Qaida occupies territory.
BP started natural gas production at the facility in 2006. The company said production there was targeted at around 870 million cubic feet per day, making it the largest facility of its kind in Algeria.