Vapor-liquid equilibria for binary solutions of polyisobutylene in C-6 through C-9 n-alkanes were obtained at 65 degrees C. Using a classic, gravimetric-sorption method, the amount of solvent absorbed by polyisobutylene was measured as a function of solvent vapor pressure. The data were interpreted by the Flory-Huggins theory and the Prigogine-Flory-Patterson theory.