Ternary liquid-liquid equilibria were predicted by the UNIFAC method for organic/aqueous biphasic systems containing amino acids and amino acid oligomers composed of glycine, alanine, phenylalanine, and tyrosine. UNIFAC was used to screen solvents for use as potential extractants, and UNIFAC-calculated distribution coefficients were compared to data obtained experimentally. UNIFAC identified some novel extractants from a larger database of solvents. Distribution into the organic phase generally increased with the degree of polymerization of the oligomers. The presence of nonpolar residues in oligomers was found to decrease extraction over hydrophobic species alone. It was concluded that the polarity of the amide backbone and the zwitterion effects were significant in reducing the hydrophobicity of the side chains.