[en] The complexation behaviour of Am(III) with 12-crown-4, 15-crown-5, 18-crown-6 and dicyclohexyl-18-crown-6 in aqueous phase has been investigated using the solvent extraction tracer technique, keeping (ligand) to (metal) ratio as high as 10⁶. As a consequence, very low complex formation constants (log β₁ = 0.21 ± 0.01) were measured. In our experimental conditions, 12-crown-4 forms 1:3 complex species, 15-crown-5 and 18-crown-6 form 1:2 species and dicyclohexyl-18-crown-6 forms 1:1 species with Am(III). The overall extraction equilibria were found to be enthalpy stabilized and entropy destabilized. (orig.)