A quaternary blend system composed of three low-T-g. semi-crystalline aryl-polyesters namely, [poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT)] and an amorphous high-T-g poly(ether imide) (PEI) was prepared and investigated using thermal and morphology characterization techniques. This study, for the first time, demonstrated miscibility and phase behavior of a quaternary blend comprising four different polymers. A single and composition-dependent Tu was found for each of all quaternary blend samples.-In addition, various thermal transition characteristics;- single and composition-dependent T-c,T-c, increasingly suppressed DeltaH(c,c) at higher PEI contents, are also indication of phase miscibility of the quaternary blend. SEM morphology characterization (3000X) revealed no discernible domains and homogeneous phase morphology in the quaternary blends was also substantiated using optical and scanning electron microscopy results.