To determine where on the Robeson plot a polymer is located, we need to be able to predict the CO 2 /N 2 and CO 2 /O 2 selectivity as well as the CO 2 permeability. The ideal selectivity α i/j for the gas pair is the ratio of the permeabilities P i and P j . Thus, we need ML models to predict N 2 and O 2 permeability as well. Because the random forest regression model is the best performing model for the CO 2 permeability, we have continued using random forest regression for the N 2 and O 2 permeability. Figure shows model predictions for the N 2 and O 2 permeability.