The equilibrium phase behavior of poly(2-ethyl-2-methylpropylene terephthalate) (PEMPT)/ Bisphenol-A polycarbonate (PC) blends is monitored as a function of polyester and polycarbonate molecular weight, composition ratio, and end-group type. Six polyesters, number-average molecular weights (Ms) varying from 4100 to 37 500, and two PCs, M(n)s of 11 000 and 21 000, are studied at PEMPT/PC composition ratios of 15/85, 30/70, 50/50, 70/30, and 85/15 (w/w). PEMPT/PC blends are found to be two phase at all but the lowest molecular weight pairs examined. Composition effects are most apparent in blends containing components with low molecular weight. Hydroxyl- and benzoate-terminated PEMPT/PC 50/ 50 blends exhibit similar phase behavior and qualitatively follow Flory-Huggins theory with enhancement in miscibility as molecular weight is decreased. Blends containing polyesters with heptafluorobutyrate end groups show substantially different phase behavior. Virtually no enhancement in partial miscibility of the components is observed as the molecular weight of the polyester is lowered. These results are explained in terms of a multicomponent interaction parameter that accounts for both midchain/midchain interactions and midchain/end-group interactions. The interaction parameter of the blend, as calculated from critical point data, is 0.044.