Vehicle air conditioning is often blamed for its 20 to 40% overconsumption of fuel and its contribution to the greenhouse effect. This is largely due to the poor energy and environmental performances of the refrigerants used. Natural refrigerants as carbon dioxide (CO2) or hydrocarbon (HC) can contribute to contain the problem. But Carbon dioxide, as a refrigerant, does not liquefy at the high pressure heat exchanger of the refrigeration loop within tropical outside temperature, due to its low critical temperature (31°C), and HC are flammable. An alternative solution appears to be the use of the mixture of carbon dioxide (CO2) and hydrocarbon (HC) which is a less flammable or non-flammable refrigerant with low global warming potential. Thus the study reviewed the state of the art concerning the use of CO2 for vehicle air conditioning and focused on mixtures of CO2 and HC which are condensable at room temperature. The investigations were carried out on mixtures of CO2 and HC with different molar fractions of CO2 (from 0 to 100%). The equation of Van Poolen et al. made it possible to predict the critical points of the different mixtures. MATLAB software was used to compute the coordinates of the critical points of the mixtures and to deduce the eligible best mixtures candidate. The investigations showed that CO2/R600a mixtures are more suitable for hot and tropical areas.