Dark fermentation for bio-hydrogen (bio-H-2) production is an easily operated and environmentally friendly technology. However, low bio-H-2 production yield has been reported as its main drawback. Two strategies have been followed in the past to improve this fact: genetic modifications and adjusting the reaction conditions. In this paper, the second one is followed to regulate the bio-H-2 release from the reactor. This operating condition alters the metabolic pathways and increased the bio-H-2 production twice. Gas release was forced in the continuous culture to study the equilibrium in the mass transfer between the gaseous and liquid phases. This equilibrium depends on the H-2, CO2, and volatile fatty acids production. The effect of reducing the bio-H-2 partial pressure (bio-H-2 pp) to enhance bio-H-2 production was evaluated in a 30 L continuous stirred tank reactor. Three bio-H-2 release strategies were followed: uncontrolled, intermittent, and constant. In the so called uncontrolled fermentation, without bio-H-2 pp control, a bio-H-2 molar yield of 1.2 mol/mol glucose was obtained. A sustained low bio-H-2 pp of 0.06 atm increased the bio-H-2 production rate from 16.1 to 108 mL/L/h with a stable bio-H-2 percentage of 55 % (v/v) and a molar yield of 1.9 mol/mol glucose. Biogas release enhanced bio-H-2 production because lower bio-H-2 pp, CO2 concentration, and reduced volatile fatty acids accumulation prevented the associated inhibitions and bio-H-2 consumption.