Expressions are derived for the second and third Kerr virial coefficients, Bk and Ck, of spherical top molecules in terms of irreducible cluster polariza-bilities, and values are calculated using the dipole-induced dipole model for argon, krypton, xenon, methane, tetrafluoromethane, neopentane and sulphur hexafluoride. For mixtures of rare gases it is shown that the collision-induced dipole moment makes a negligible contribution to Bk- The effect of the choice of intermolecular potential function on the calculated second Kerr virial coefficients is also demonstrated. It is found that the predominant contributions to Ck arise from the pair polarizability, and that the triplet polarizability is only of minor importance. © 1979 Taylor & Francis Group, LLC.