Surface diffusion data previously measured for different compounds, mobile phase solvents, stationary phases, and temperatures in reversed-phase liquid chromatography (RPLC) were reevaluated to derive information related to the mechanism and characteristic features of surface diffusion. First, a comparison of the surface diffusion coefficient (D-s) and the corresponding molecular diffusivity (D-m) suggests that the dependence of D-s on the RPLC conditions is a consequence of that of D-m. There is a correlation between surface diffusion coefficients and molecular diffusivity. Second, we showed that D-s correlates with the adsorption equilibrium constant (K) and the isosteric heat of adsorption (Q(st)). These two parameters represent the intensity of the adsorptive interactions between the sample molecules and the surface of the stationary phase. Finally, the ratio Ds/Dm increases with decreasing K and -Q(st) and D-s becomes of the same order of magnitude as D-m when the adsorptive interactions become small. These results imply that surface diffusion should be regarded as molecular diffusion restricted by the influence of adsorptive interactions. Other information on surface diffusion was also obtained. The value of D,. extrapolated at Q(st) = 0 is not equal to D-s The difference between the two coefficients depends on the experimental conditions, e.g., the nature of the organic modifier in the mobile phase or the surface density of the C-18 alkyl ligand on the stationary phase. Our results demonstrate that surface diffusion is fundamentally related to molecular diffusion.