A combined experimental and computational thermodynamic study of 4-ethylmorpholine was undertaken in this work to resolve large discrepancies between the two vapor pressure data sets reported in the literature. As no thermodynamic tests were capable of revealing which of the published data sets are in error, new vapor pressure measurements by the static method and determination of liquid-phase heat capacities by Tian-Calvet calorimetry were carried out in this work. Ideal-gas heat capacities, an indispensable input for testing the thermodynamic consistency of vapor pressures, were obtained by combining statistical thermodynamics and quantum chemical calculations. Although the vapor pressure determined in this work was found to be in reasonable agreement with one data set published previously (deviations within 10%), both literature data sets show significant inconsistencies with heat capacity data. Therefore, the recommended vapor pressure equation for 4-ethylmorpholine was developed solely based on the vapor pressure and heat capacity data obtained in this work, which were treated simultaneously to ensure a thermodynamically consistent description of vapor pressure in the temperature range 243-298 K with the estimated expanded (k = 2) uncertainty of 0.5%.