Technical Abstract: Nonwetting-phase relative permeabilities may be predicted from retention- curve data using a variety of analytical models as well as pore-scale network models.Analytical models that do not account for a discontinuous nonwetting phase fail to predict relative gas permeabilities, while models that account for this phenomenon result in very good predictions.Prediction nof relative permeabilities with these analytical models requires stipulation of at least one additional parameter after fitting the retention curve.And these analytical models cannot predict absolute permeabilities without some permeability data.Comparisons of predicted gas permeabilities to measured data for two sandy soils indicate that the network model used provides good estimates of both relative and absolute permeabilities, and can accommodate a discontinuous gas phase, without any parameters beyond those needed to fit the retention curve.While the predicted magnitude of the hysteresis effect in the relative gas permeability functions was not large enough, the predictions obtained with the network model were much better than those calculated with the only analytical model that can be used for prediction of relative permeabilities on the basis of retention data only.