The phase behavior of binary blends of linear main-chain aliphatic polyesters and blends of poly(caprolactone) with caprolactam/caprolactone copolymers has been investigated both experimentally and theoretically within the terms of a binary interaction model. A relatively small and unfavorable value of the methylene-ester segmental interaction parameter, chi(AD), estimated previously from studies of polyamide/polyester blends allows for entropically driven miscibility of blend constituents possessing considerable chemical dissimilarity. Although a reasonable correlation between experiment and calculations has been obtained, the analysis also provides a discussion of how configuration, or the arrangement of chemical species or segments, may affect the parameters used.