Abstract: The present document describes a process for production of hydrogen gas (H2) from fermentation of crude glycerol with a hydrogen producing microorganism in a bioreactor. The process comprises the step of introducing a volume of crude glycerol in a fermentation mixture which comprises a fermentation medium comprised of crude glycerol and hydrogen producing microorganisms under a fermentative hydrogen production condition, and then removing a volume of the fermentation mixture equal to the second volume of the crude glycerol, to maintain constant the total volume of the fermentation mixture.