Strikers have blocked petrol terminals at Fos-sur-Mer and Lavera for the past 10 days, causing petrol disruptions as far as Corsica.
The strike, bolstered by the unions, will extend to the refinery in Etang de Berre on Thursday. Employees at Ineos Refinery (formerly BP) are also planning to join the strike.
Oil workers are also protesting the nationwide French pension reforms.
On Wednesday, port authorities in Marseilles said that they were continuing dialogue in a "difficult climate".
Meanwhile, Corsica is expected to receive petrol Thursday night from an oil ship chartered by Sardinian oil companies.