Literature data for homologous series of nonionic and ionic surfactants, such as CnOH, CnEO Tritons, CnSO4Na, and CnEOmSO4Na, were analyzed on the basis of the Frumkin and reorientation models. The thermodynamic quantities obtained from the reorientation model agree best with the experimental data. They yield the standard free energy of adsorption which can be split into contributions from the alkyl chain, and the polar head group. An additional contribution to the increment of the polar group DeltaG(P)(0) from m EO groups DeltaG(EOm)(0) is extracted which can be accounted for by DeltaG(EOm)(0) = -2.35rootm kJ/mol. The standard free energy of adsorption is well understood by the increment method used. (C)2002 Elsevier Science (USA)