Properties of monolayers, formed by soluble surfactants of widely differing chemical structure, have been investigated by surface light scattering over the frequency range omega(0) 10(4)-10(5) s(-1). For all surfactants studied, negative values for the dilational viscosity (epsilon’) were found, implying that the dilational waves are destabilized. This behavior is consistent with the presence of an adsorption barrier (Hennenberg, M.; ct al. J. Colloid Interface Sci. 1992, 150, 7). This barrier can be altered by mixing dodecane into C(16)TAB and C(10)E(8) monolayers, and epsilon’ then assumes positive values. Furthermore, the characteristic time for monomer adsorption into the pure film (tau(ads)) may be estimated as about 10(-5) s(-1).