Distribution of formic, levulinic and acetic acids between water and Alamine 336, a mixture of tertiary aliphatic amines, dissolved in various (proton-donating and -accepting, polar and nonpolar) diluents, as well as a comparison with the extraction equilibria of pure diluent alone are studied at 25 degrees C. The influence of the acid structure over distribution is evaluated through comparing the extractabilities of five acids containing different functional groups, namely, formic, levulinic, acetic, valeric and nicotinic acids. The results were correlated using a modified linear solvation energy relation (LSER) and various versions of the mass action law namely, a chemical modeling approach and a modified version of the Langmuir equilibrium model comprising one or two acid-amine complex formations. Details underlying some aspects of selection of an appropriate algorithm for fitting the data are discussed. Finally, the reliability of the proposed extraction models is analyzed statistically on the basis of the overall loading factor of amine, Z(t), using a log-ratio objective function.