The equilibrium phase relationships near the liquidus line of the system Cu2O-CuO-O2 (a part of wider system Cu-O) were determined under pure oxygen pressure from 0.001 to 11 MPa by three experimental methods: differential thermal analysis (DTA), thermogravimetry (TG), and thermobarometry (TB). The coordinates of the eutectic point between solid Cu2O and CuO were found to be P O 2=0.069±0.001 MPa and T=1364±1 K. It was proved experimentally that, at least at temperatures up to 1526 K and oxygen pressures up to 11 MPa, CuO melts incongruently with liberation of gaseous oxygen and with the temperature dependence of P O 2 obeying an Arrheniustype equation. The conditions for congruent melting of CuO were analyzed using the model, and it was found that congruent melting of CuO should occur at ≈ 1620 K under oxygen pressure ∼1000 MPa.