All trace of the four-day siege — which saw workers from Japan, the Philipines, Britain, Norway and the United States killed — has long been cleared away at the sprawling desert facility 1,300 kilometres (800 miles) southeast of Algiers.
“They are 40 martyrs. I am full of emotion, I knew a lot of these people,” said Abdelmoumen Ould Kaddour, the CEO of Algeria’s Sonatrach, that runs the site with Norway’s Statoil and Britain’s BP.
The assault — which left 29 attackers dead — was claimed by one-eyed Algerian jihadist Mokhtar Belmokhtar, a former head of Al-Qaeda in the Islamic Maghreb.
At a ceremony the name of the victims were read out and a wreath laid after the recital of the Fatiha, the opening passage of the Koran.
Among the roughly 100 workers gathers were some who had survived the siege.
“We are going to mark five years since the attack and then go back to work,” one worker who was held hostage for three days told AFP.
“It is hard for us and our families are anxious. Some people cannot escape the memories and are still disturbed by them. But life continues.”
Since the attack the number of expats working on site has been reduced dramatically and the firms running the remote facility insist security has been ramped up.
To access the plant — just 80 kilometres from the border with chaos-riven Libya — you have to pass through several checkpoints and series of barriers.
There have been several international probes into the attack, which was claimed as revenge for French operations in Mali.
Four men are facing trial in Algiers over the raid.
The suspected masterminds, including Belmokhtar, have not been caught.