Departures from the geometric mean assumption for the interaction energy between unlike polymer repeat unit pairs i/j computed from experimental data, were correlated with the molecular connectivity indices for the repeat units. The effects of various factors on the correlation results were investigated. A better correlation is obtained when terms involving the solubility parameters for the repeat units are included. This empirical scheme provides a viable way to predict interaction energies, and, thus, blend phase behavior and interfacial parameters. The limitations of this scheme and possible ways to improve the correlation are discussed. (C) 2003 Elsevier Ltd. All rights reserved.