Critical lines for the six binary mixtures ethane + propane, ethane + n-butane, carbon dioxide (CO2) + dinitrogen monoxide (N2O), N2O + ethane, N2O + propane, and N2O + sulfur hexafluoride (SF6) were measured by means of the flow method, where the critical points are determined directly by the visual observation of the disappearance and reappearance of the phase border. These data, which provide information about the location and boundary of the two-phase region of the concerned systems, can be used to examine and develop thermodynamic models like the Predictive Soave-Redlich-Kwong (PSRK) group contribution equation of state. In this work, new PSRK group interaction parameters for the combinations alkane + N2O, CO2 + N2O, and N2O + SF6 were obtained by the correlation of the critical and vapor-liquid equilibrium (VLE) data.