A method of storing CO2 in a porous and permeable hydrocarbon reservoir having at least one injection well and at least one production well penetrating the reservoir, by recovering a produced fluid stream including produced hydrocarbons, produced water, and produced CO2 from the production well; passing the produced fluid stream to a production facility where a produced vapor stream of carbon dioxide and volatile hydrocarbons is separated from the produced fluid stream; compressing the produced vapor stream to above the cricondenbar for the produced vapor stream; cooling the compressed stream to form a cooled stream that in a dense phase state; importing a CO2 stream to an injection facility wherein the imported CO2 is either in a liquid state or a supercritical state; mixing the cooled stream with the imported CO2 stream thereby forming a co-injection stream; and injecting the co-injection stream into the hydrocarbon bearing reservoir from said injection well.