The plant was raided in January last year by Islamist militants, who killed 40 people, including five Statoil employees. There were almost 800 people at the plant, when the attack happened, according to Statoil.
"The decision to resume ordinary operations at In Amenas is the result of a thorough and stepwise process of identifying necessary security measures, implementing them and validating that they are in place and operational," Statoil's executive vice president for international development and production Lars Christian Bacher said.
The Norwegian company kept its employees away from the plant, which it operates as a joint venture with BP and Algeria's Sonatrach, since the attack, which was ended after four days as Algerian forces reclaimed the facility.
"We will now, in cooperation with our partners, continue our systematic work to maintain the high level of the security measures, to ensure that we have a good understanding of the security threats and adjust our security measures as required," Bacher added.
The In Amenas plant produced about 11.5 percent of Algeria's natural gas before the attack, according to figures from news agency Reuters.