Isobaric vapor liquid equilibrium (VLE) for methanol (1) + water (2) + tetramethylammonium bicarbonate (TMAB) has been measured at pressures of 66.52 kPa and 37.60 kPa. The binary data for methanol + water were correlated by the Wilson model at subatmospheric pressures. All of the experimental results of the binary system passed the thermodynamic consistency test by the area test of Redlich-Kister and the point test of Van Ness et al. The Ohe's preferential solvation model was used to correlate the VLE data of the ternary system. The experimental results of the ternary system show that TMAB has a salt-out effect on methanol, and this effect enhances with increasing the concentration of TMAB.