The general nature of the Gibbs ensemble method allows for easy extensions to a wide variety of equilibrium processes in addition to the standard vapor-liquid equilibrium calculation. In this work, Gibbs ensemble Monte Carlo is used to determine the effect of water co-adsorption of the adsorption behavior of chemical warfare agents sarin and soman. These results are compared to similar calculations performed on dimethylmethylphosphonate (DMMP), a non-toxic simulant commonly used in experimental adsorption studies in place of sarin.