A statistical theory which describes the effect of changes in antifoam concentration on foamability has been formulated. The theory produces simple generalizations which are readily verifiable by experiment. Thus plots of foam volume against, the logarithm of antifoam concentration for given surfactant solutions and given methods of foam generation should be isomorphous, regardless of the nature of the antifoam. Foam generated by shaking cylinders and by the static Ross-Miles technique confirms this prediction. In the ease of foam generated by passing gas through porous frits, theory predicts simple exponential dependence of foam volume on antifoam concentration. This is shown to be consistent with literature results for foam generation by this method. Theory has been generalized for mixtures of noninteracting antifoam dispersions of different effectiveness. From a knowledge of the antifoam concentration dependence of the foam volume for each constituent dispersion in a given surfactant solution and for a given method of foam generation, theory predicts that we should be able to calculate the corresponding behavior for the mixed dispersion, This has been confirmed by experiment.