A hybrid rheological approach utilizing thermal analysis, microscopy, and oscillatory viscoelastic measurements is presented here for estimating the interfacial tension, gamma(12), of a partially miscible polymer mixture. The mixed composition of each of the bulk phases affects its complex modulus and T-g, along with gamma(12) and the blend morphology, as a whole. The inverted form of an appropriate rheological model connecting all the above properties is used to evaluate the interfacial tension. It is demonstrated that partial miscibility also affects the interfacial tension predictions obtained by the harmonic method.