Reactive extraction of propionic acid from aqueous solution containing 0.05 to 0.4 kmol/m(3) acid using tri-n-butylphosphate (TBP) (organophosphorous compound), tri-n-octylamine (TOA) (tertiary amine), and Aliquat 336 (quaternary amine) as extractants in 1-octanol was studied. The comparison among the different categories of extractants was made. The order of extraction power was found to be TOA > Aliquat 336 > TBP with K-E values of 25.67, 3.58, and 2.36 m(3)/kmol, respectively. The highest value of equilibrium complexation constant (25.67 m(3)/kmol) and distribution coefficient (14.09) of TOA suggested it to be the best extractant among the three. The greatest support to highest recovery was also due to the choice of diluent for the system. 1-Octanol was an active diluent which provided good solvation of the acid-extractant complexes. In all the extractions (1: 1) acid-extractant complexes were formed with loading ratios less than 0.5, except in Aliquat where values higher than 0.5 were also obtained. This led to the definition of an another equilibrium constant (K-E(2:1)) as (2:1) acid-Aliquat complexes were formed, with the value of K-E(2:1) = 26.54 (m(3)/kmol)(2).