Equations for the densities of seawater in the abyssal zone and of CO2 hydrate are derived based on measured densities of seawater at intermediate depths and on the hydrate crystalline structure. Predictions from the derived equations agree excellently with the measured densities of seawater and CO2 hydrate. It is found that CO2 hydrate contains fewer than the stoichiometric number of CO2 molecules, and thus the density of CO2 hydrate is smaller than the value widely used in the literature. Therefore, albeit denser than seawater above the abyssal zone, CO2 hydrate may become less dense than abyssal seawater. A neutral buoyancy depth may exist in the abyssal zone in about 60% of the areas of the Atlantic, Pacific and Indian Oceans. In these areas, CO2 hydrate deposited in the ocean cannot reach the seabed. The most economic depth for hydrate disposal is the minimum depth for hydrate formation, which is about 500 m below the surface in many oceans. Since CO2 hydrate is unstable in seawater which is unsaturated with CO2, no permanent hydrate phase will exist in the ocean where the concentration of CO2 is negligible. If the disposal depth is chosen at 500 m and the sizes of hydrate particles are not very large, then in more than 90% of the areas of the three oceans (excluding adjacent seas), hydrate particles deposited in the ocean will dissolve fully before reaching the neutral buoyancy depth or the seabed, if the neutral buoyancy depth does not actually exist.