This work consists in studying the influence of the lead inhibitive concentration on the biological treatment of wastewater of the oil well drilling by a bioreactor filled with an inert solid support. The concentrations varied from 80 to 100 mg/L for reaching the inhibitive concentration of the gas-oil biodegradation process. The experimental results showed that the best yield of the gas-oil elimination of 80.84% was obtained for the lead initial concentration equal to 80 mg/L and it was about 78% with the initial concentration in lead equal to 100 mg/L.