This work involved a series of studies on liquid–liquid phase equilibrium in chemical non-equilibrium and chemical equilibrium states, i.e. corresponding to chemical equilibrium heterogeneous compositions, at a fixed temperature and pressure in a system consisting of n-butyl alcohol and n-butyl acetate as potential fuel components. Phase equilibrium was studied for two binary (n-butyl alcohol–water and n-butyl acetate–water), three ternary (acetic acid–n-butyl alcohol–water, acetic acid–n-butyl acetate–water, and n-butyl alcohol–n-butyl acetate–water) and one quaternary (acetic acid–n-butyl alcohol–n-butyl acetate– water) systems at 303.15 K and 101.3 kPa. Chemical equilibrium heterogeneous compositions were found for the acetic acid–n-butyl alcohol–n-butyl acetate–water system under the same conditions. Chemical equilibrium was reached in the presence of a catalyst (hydrochloric acid). All results are presented in twodimensional and three-dimensional composition spaces. For further visual representation of the obtained data, the compositions of chemical equilibrium phases are presented in the square of concentration α-variables. A comparative analysis of the obtained compositions was carried out. Correlation analysis was performed using the NRTL model, taking into account vapour–liquid equilibrium data for binary mixtures reported in the literature. Thus, we attempted to thoroughly estimate the possibility of mutually correlating vapour-liquid and liquid–liquid equilibrium data for the studied system. Calculations showed sufficient agreement between the experimental values and the calculated data.