In the Onsager model on the basis of statistical calculation of the cavity radius by the method proposed by Linder and Hoernschemeyer using experimental data for the radial distribution function g(r) in liquids, the molecular polarizability changes Δα under phase transition from gaseous to liquid state are evaluated for eight substances: noble gases, CH4, CF4, and water. For all liquids with the exception, perhaps, of helium and neon (everything depends on the accuracy of the experimental data for the dielectric constant ε and the polarizability α0 of noninteracting molecules in gases) Δα proves to be positive. Contributions of dipole and overlap effects to Δα in liquid He, Ne, and Ar are discussed on the basis of the approximate calculation of the dipole part using Slater one-electron orbitals and theoretical results for the two-body contribution to electron overlap. The Onsager model allows one to calculate also the Kirkwood fluctuation correction to the Clausius–Mossotti function and values of some three-body integrals.