The extraction equilibria of the type 2 ternary systems containing (water + isovaleric acid + solvent) have been investigated at T = (298.2 +/- 0.1) K and P = (101.3 +/- 0.7) kPa. Aromatic solvents xylene, chlorobenzene and benzyl ether give the largest distribution ratios and separation factors, as compared to 1-phenyl ethanol, cyclohexanol and 1-decanol. The distribution data have been subjected to formulation of an optimization structure for an effective acid separation. The optimization approach uses a derivative variation method to efficiently identify the optimization range through analyzing the first order derivatives of the optimized quantity and the non-linear deviation profile of the derivative value. Some aspects of selection of an appropriate criterion for designing optimum extraction are discussed.