In this paper, the performance and the reliability of a new apparatus to determine the critical properties of pure components and gas/gas binary mixtures (i.e., mixtures for which the two components are gaseous at ambient conditions) with a known overall composition are studied. Critical temperatures (Tc) and critical pressures (Pc) of binary mixtures composed of carbon dioxide + a light nalkane (CO2 + n-propane, CO2 + n-butane) or of two light nalkanes (n-propane + n-butane) are measured. For the first time, the ability of our apparatus to determineusing the dynamic modethe critical loci of gas/gas binary systems is tested. The critical points are visually determined by observing the critical opalescence and the simultaneous disappearance and reappearance of the meniscus in the middle of the view cell which withstands operations up to 673 K and 20 MPa. The experimental critical data in this work are compared with previously measured literature data and with values predicted by the PPR78 thermodynamic model.