The intrinsic viscosities of poly(ethylene glycol)/poly(ethylene oxide) (PEG/PEO) blends have been measured in benzene as a function of blend composition for various molecular weights of PEO at two different temperatures (293.15 K and 303.15 K). In order to predict the compatibility of polymer pairs in solution, the interaction parameter term, Delta b, and the difference between the intrinsic viscosities of the polymer blends and the weight average intrinsic viscosities, Delta[eta], of the two polymer solutions taken separately are used. The effects of both temperatures and molecular weight of the blend components on the extent of compatibility was elucidated.