The effect of inert gases, such as helium, air, and sulfur hexafluoride, in breaking the formic acid-water azeotrope by gas-gap membrane distillation process is theoretically investigated under the process relevant operating conditions. A Stefan-Maxwell-based mathematical model that includes all necessary vapor-liquid equilibrium, heat, and mass relations is used for this purpose. According to the model predictions, heavy inert gases such as sulfur hexafluoride help more in breaking the azeotrope than Lighter ones such as air and helium. This phenomenal behavior is discussed along with the effect of other associated process parameters.