Ahstraet-Tracer diiusion coef%ients are determin ed with the Taylor-Aris dispersion method for benzene, toluene, p-xylene, mesitylene, naphthalene and phenanthrene in liquid a-hexane along the vapour-liquid coexistence curve from 333.2 to 4854K and in supercriticaf n-hexaue at 507.4, 5220, 533.3.543.2K and several pressures. A rough-hard-sphere model is found to represent quite well (to within f 6 %) the ohserved tracer diffirsivities in the density region where computer simuktion results for OF/Of2 are available, i.e. 1.5 Q V/V, c 3. Furthermore, Hildebraad's free volume model together with the excluded-volume effect provides the basis for a general linear relationship between D,2 V,,, and Y for trscer diffusion in liquid nhexane up to its critical temperature. For diHirsion in the supercritical region two definitions of reduced tracer diiusivity, one bssed on the rough-hard-sphere. theory of tracer difliision and the other on the extension of Helfand-Rice cm-responding state principk for self-diffusion, permit general&d correlations that are capable of representing the experimental results in both supercritical n-hexane and carbon dioxide to within f4% on average. _ _ Taylor, G. I., 1953, Dispersion of soluble matter in solvents flowing slowly through a tube.