A liquid-liquid-solid jet reactor has been developed to convert liquid CO2 and seawater into solid hydrate at intermediate ocean depths. The objective was to identify the hydrodynamic and thermodynamic conditions at which negatively buoyant, consolidated CO2 hydrate particles are generated. This effort will be useful in developing the technology for CO2 ocean carbon sequestration. Formation of CO2 hydrate has been investigated using a coflow reactor in a 72-L high-pressure vessel. Scaleup issues of the hydrate reactor have also been investigated. The scale-up version of the reactor consisted of either a single capillary or an array of multiple capillaries used to disperse liquid CO2 in water or water in liquid CO2. Several capillary sizes and configurations were tested in both distilled and saline water. The scaleup design increased CO2 injection to ~4.5 L/min, representing a 20-fold increase from previously used geometries. Data were obtained at different CO2 and water flow rates and for pressures and temperatures equivalent to those of intermediate ocean depths. Although negatively buoyant particles were effectively formed with distilled and saline water, the physical and hydrodynamic characteristics of the product depended heavily on the geometric configuration and flow rate conditions of the reactor. Laboratory results were supported by experimental data obtained in the ocean in April 2006, at depths between 1000-2000 m. Comparisons between laboratory and field data, as well as differences between CO2 sprayed in water and water sprayed in CO2 in both laboratory and field experiments will be presented and discussed.