In this paper, it is shown that the symmetrically normalized activity coefficient of the solute in the bulk solution, y(B)(b), makes a non-negligible contribution to the standard Gibbs energy of adsorption of solute from the bulk at the surface of binary liquid mixtures, Delta(ads)G(0). With a view to defining this change with practical purposes, we selected the pure solute and a surface pressure pi of 1 mN m(-1) as standard states for the bulk and surface phases, respectively. Besides, we assumed availability of data in the highly dilute region, where the two-dimensional ideal equation of state holds. In this way, Delta(ads)G(0) = -RTln(pi/gamma(B)(b)x(B)). When gamma(B)(b) is taken into account, Traube's rule (that In(pi/x(B))x(B -> 0) increases linearly with chain length in the water + 1-alkanol series) does not imply that Delta(ads)G(0) increases linearly with chain length. On the contrary, together with the fact that in this series 1n(y(B)(b,infinity)) increases with chain length at the same rate as 1n(pi/x(B))(xB -> 0), Traube's rule implies that Delta(ads)G(0) is constant in this series. This can be interpreted in molecular terms as indicating that in highly dilute solutions the hydrocarbon chain of alkanol molecules at the surface does not lie in or on the surface (as is implied by a linear increase in Delta(ads)G(0) with chain length), but resides completely in the gas phase, as is now known to be true. The constancy of Delta(ads)G(0) also explains why water + 1-alkanol systems share the same pi versus gamma(B)(b)x(B) curve except at high surface concentrations, where the degree of discrepancy is in any case limited by the small differences in surface tension among the pure alkanols. We conclude by using the "Extended Langmuir" model of surface behaviour to Split Delta(ads)G(0) into five distinct physically meaningful contributions. (c) 2004 Elsevier B.V. All rights reserved.