According to an embodiment, there is provided herein a system and method wherein knowledge of the syngas fermentation is combined with standard instrumentation to provide a stable control of gas supply to automatically poise the fermentation to provide both high conversion of CO and H2, and high selectivity for production of ethanol. The control is based on an automatic feedback loop that corrects for operational imbalance and maintains a stable continuous fermentation required for commercial operation. In a further embodiment, feed of syngas to ethanol fermentation can be optimally controlled using the pH of the broth as the input variable for flow control of the gas. This concept will automatically maintain the correct supply of syngas to the fermentation, and provide stable operation at optimal rates.