The court overturned earlier acquittals, 11 years after the blast that tore apart the AZF plant in Toulouse with the force of a 3.4-magnitude earthquake. Some 2,000 people were injured.
The appeals court ruled Monday that negligence by factory chief Serge Biechlin "created or contributed to the situation" that caused the accident.
It said Total subsidiary Grande Paroisse was his employer and also responsible.
Biechlin's defense said he would take the case to the Supreme Court.
The blast occurred 10 days after the Sept. 11 terror attacks in the United States and raised fears of terrorism but proved to be an accident.
(Copyright 2012 by The Associated Press. All Rights Reserved.)