Pressure-mole fraction phase diagrams for the CO2-water system at temperatures between 278.15 and 298.15 K and pressures up to 30 MPa, which correspond to those of ocean waters at depths to 3000 m, are developed based on the literature data and experimental results obtained by the authors. The resultant phase diagrams can serve as a basis for analyzing the phase behavior of liquid CO2 and CO2 hydrate disposed of in the ocean as a means to mitigate global warming.