An additive scheme for resolving average molecular electric dipole polarizabilities into atomic contributions, based on the acceleration gauge for the electric dipole, has been applied to a series of methyl and ethyl derivatives, CH3-X and CH3-CH2-X. Extended calculations have been carried out to test the reliability of the partition method. Gross atomic isotropic contributions have been evaluated for carbon, hydrogen, and heteroatoms, showing a good degree of transferability from molecule to molecule. The theoretical values of atomic polarizabilities can be used to predict fairly accurate average polarizabilities of higher homologous molecules in the series of X-substituted alkanes. (C) 2001 American Institute of Physics.