Vapor-liquid equilibria are reported for the following four systems: 2-phenylpropionaldehyde + phenol at 100 degrees C and 150 degrees C; propylene glycol monomethyl ether + nitroethane at 40 degrees C and 80 degrees C; dimethyl ether + propylene at -20 degrees C and 20 degrees C; and n-butyric acid + propionic acid at 100 degrees C and 140 degrees C. The system pressure and temperature were measured at several charge compositions along a given isotherm for each system. Equilibrium vapor- and liquid-phase compositions were derived from the measured PTx data using the Soave equation of state to represent the vapor phase and the Wilson or three-parameter Redlich-Kister activity coefficient model to represent the liquid phase. Vapor-phase dimerization of the carboxylic acids was accounted for in reducing the n-butyric acid + propionic acid PTx data. A single Txy data point was also measured for this system at each temperature by withdrawing and analyzing multiple samples from the equilibrium vapor and liquid phases.