In this study, the reaction equilibrium of the reversible esterification of acetic acid with 1-butanol giving 1-butyl acetate and water was investigated. The entire composition space including the miscibility gap was covered at temperatures relevant for technical processes (353.15 K to 393.15 K). The experiments were carried out in a multiphase batch reactor with online gas chromatography and in a batch reactor with quantitative 1H NMR spectroscopy, respectively. The thermophysical database available in the literature was complemented by measurements of liquid−liquid and vapor−liquid equilibria. On the basis of that comprehensive data, thermodynamically consistent models of the reaction equilibrium were developed which predict the concentration dependence of the mass action law pseudoequilibrium constant, Kx. The following different modeling approaches are compared: the GE models NRTL and UNIQUAC as well as the PC-SAFT equation of state and the COSMO-RS model. All of them can successfully be used, the CO...