Our theory for the interfacial properties of compressible binary polymer systems [J. Chem. Phys. 98, 8994 (1993)] is generalized to treat phase separated asymmetric binary blends. The theory is illustrated by using a Sanchez-Lacombe approximation for the homogeneous system free energy and a Cahn-Hilliard-de Gennes expression for the square gradient contribution. These two ingredients enable the same theory to describe both the compositions of the coexisting phases and the interfacial properties. The coupled equations for the two concentration profiles are numerically unstable, and our perturbation-variational method for symmetric blends is extended to treat blends with asymmetry due to differing polymerization indices and/or interaction parameters. The zeroth order approximation, which uses a hyperbolic tangent interpolation between the generally different densities iri the coexisting phases, is found to be extremely accurate in predicting the interfacial tensions and widths. Illustrations of the theory are provided for systems with upper and with lower critical solution temperatures, as well as with hour-glass miscibility gap type phase diagrams. The higher order perturbation-variation contributions mainly affect the total density variation through the interface, exhibiting several different patterns of density redistributions to lower the interfacial free energy. Computations are also provided for the pressure dependence of the interfacial properties.