Compositions of coexisting phases (liquid-liquid equilibrium), solubility, and critical states for the quaternary acetic acid-n-butyl alcohol-n-butyl acetate-water system were carried out at 328.15 K and 101.3 kPa. The results of the work include topological analysis of phase diagrams. The data on liquid phases were determined by gas chromatography analysis. Solubility results and critical compositions were obtained by a "cloud-point" technique method. Simulation was performed using a nonrandom twoliquid model. Calculated results are in sufficient agreement with experimental data. A comparative analysis of experimental, calculated, and literature data was carried out for binary, ternary, and quaternary mixtures. The location of the critical compositions at different temperatures in the concentration space is discussed. The corresponding phase diagrams are constructed in 2D and 3D concentration spaces. The features of each of the phase diagrams are discussed.