Data needed for evaluation of ocean CO 2 -sequestering technologies include the solubility of CO 2 and density of CO 2 hydrate at 30 MPa. Theses were measured using a high-pressure facility suitable for simulating pressure and temperature conditions 3000 m beneath the ocean surface. The solubility decreases linearly with decreasing water temperature, which is opposite to the temperature dependence in the non-hydrate region. The measured solubility agrees with the published value for the non-hydrate region at an equilibrium temperature of 12 °C. The hydrate density was estimated from pressure drop, temperature increase, and concentration changes, followed by precipitation of CO 2 hydrate. The estimated CO 2 hydrate density varies from 1.11 to 1.09, depending on the fraction of CO 2 in hydrate form.