Ethanol and oxygen containing gases are mixed in a T-junction at elevated pressure and then passed into a fused silica microcapillary, located in a heating block. Inside the microcapillary a Taylor flow of alternating liquid and vapor segments is formed. The thermodynamic equilibrium composition of the liquid and vapor segment depends on pressure and temperature. Their compositions are measured inside the microcapillary using in situ Raman spectroscopy. The main results obtained therefrom are temperature-composition (Tx) diagrams at conditions relevant for combustion engines [p = (3 to 8) MPa; T = (303 to 473) K]. Isothermal vapor-liquid equilibria (VLE) data are derived and given in pressure-composition (px) diagrams. The investigation of different gas mixtures containing oxygen and nitrogen allows furthermore the illustration of VLE data at constant pressure and temperature in ternary diagrams. The obtained results are compared to scarce literature data. An equation of state (Peng-Robinson EOS) is furthermore adjusted to the measured results.