An acoustic technique was applied to investigate the critical behaviour Of CO2 + N(C2H5)(3). This study is part of a major programme on the determination of the critical behaviour of a series of tertiary amines in supercritical CO2 Measurements of the critical temperature T-c and pressure p(c) of the binary mixture Of xCO(2) + (1 - x)N(C2H5)(3) were performed restricted to the region richer in carbon dioxide, in the CO2 mole fraction range 1-0.911. The Peng-Robinson equation of state with conventional mixing and combining rules, was used to correlate the binary experimental data. The course of the whole binary critical line was extrapolated. Additionally, this paper briefly reviews the experimental methods for determining critical properties. The theoretical basis of our acoustic method and the systems studied are discussed.