Isothermal (vapor + liquid) equilibria of (acetone + tetrahydrofuran), (tetrahydrofuran + acetonitrile), (tetrahydrofuran + 1,2-dichloroethane), and (acetonitrile + 1,2-dichloroethane) have been measured at 302.15 K using the total-pressure method. The results are analysed by Barker's method with Wilson, NRTL, and UNIQUAC equations. All three are found to represent the results satisfactorily for the four mixtures. (Tetrahydrofuran + 1,2-dichloroethane) shows negative deviations from ideality; the other three show positive deviations. (Acetonitrile + 1,2-dichloroethane) and (acetone + tetrahydrofuran) form azeotropes. © 1984.