Lowering the redox potential of the growth medium is a critical step in the cultivation of obligate anaerobes for production of biofuels from synthesis gas. In this study, the simultaneous effects of reducing solutions (sodium sulfide and/or cysteine-HCl) and initial medium pH on the fermentation of synthesis gas using Clostridium ljungdahlii was investigated. The results suggested the plausible provision of more electrons into the culture in the presence of 5.07 mM cysteine-HCl at the medium pH 5.9. This culture demonstrated enhanced ethanol production (48%) and ethanol to acetate production ratio (24%) compared to the cells cultivated in standard growth medium recommended by ATCC.