In this series of publications, experimental results for the Liquid-liquid equilibrium in organic/aqueous two-phase systems containing a tertiary amine (tri-n-octylamine) and two carboxylic acids (acetic and/or oxalic and/or citric acid) are presented and compared to model predictions. This second part examines with methylisobutylketone as the organic solvent. Experimental results are reported for 298.15 K. A model was used to predict the liquid-liquid equilibrium. All model parameters were determined from experimental results for the partitioning of the single carboxylic acids between water/(methylisobutylketone + tri-n-octylamine) phases. The model predictions agree qualitatively with experimental results. When a mixture of acetic and citric acids or acetic and oxalic acids is extracted, the predicted partitioning of the acids agrees quantitatively with the experimental results. However, when citric acid is extracted together with oxalic acid, experimentally determined distribution ratios are higher than predicted, particularly for citric acid. Quantitative agreement is achieved by assuming the formation of mixed acid complexes (i.e., complexes containing two different acids).