A method and system for delivering high pressure, subcooled liquid carbon dioxide. An insulated tank having a height greater than its internal diameter holds liquid CO.sub.2 to a depth of at least about 6 feet, and high pressure, subcooled liquid CO.sub.2 is delivered from a lower outlet of the tank. CO.sub.2 vapor is condensed in the upper region to maintain a desired high pressure, e.g., about 290-310 psi., at the top of the tank. By withdrawing liquid CO.sub.2 from an upper region in the tank, subcooling it by heat exchange and returning subcooled liquid CO.sub.2 to a lower region, a thermocline region is created at least 2 feet below the surface, and above which equilibrium high pressure liquid CO.sub.2 exists. Heat exchange is efficiently carried out during off hours using liquid carbon dioxide to chill the condensed refrigerant from an existing auxiliary mechanical refrigeration unit.