Vapor-liquid equilibria (VLE) measurements have been performed for several binary polymer + solvent systems at 318.15 K using a vapor pressure osmometry (VPO) method in the semidiluted polymer concentration range. The polymers were poly(ethylene oxide) dimethyl ether 250, poly(ethylene oxide) dimethyl ether 500, poly(ethylene oxide) dimethyl ether 2000, poly(ethylene oxide) 400, and poly(propylene oxide) 400, and the investigated solvents were water, methanol, ethanol, acetonitrile, and 2-propanol. The variations of the activity of solvents with the polymer molar mass and type of polymer and solvent were investigated, and the results have been interpreted in terms of the solvent/polymer interactions. In the second part of this work, the segment-based local composition models, nonrandom two-liquid (NRTL) and Wilson, as well as the Flory-Huggins model were used to correlate the experimental activity data.