A method for the decontamination of fluid (liquid or supercritical) carbon dioxide fluid, especially of hydrocarbon contaminants, down to ≦100 ppb concentration are described. The critical component is a high silica zeolite, preferably a high silica Y-type zeolite, ZSM-5 or a high silica mordenite, which in a variety of physical forms is capable of decontaminating such fluid CO2 to ≦100 ppb, ≦10-50 ppb, or ˜1 ppb, without being detrimentally affected by the supercritical operating environment. The high silica zeolite may be produced by the removal of alumina from a natural or synthetic zeolite while retaining the desirable zeolite structure, to a silica:alumina ratio of from 20-2000:1. Preferably the zeolite is disposed in separate quantities in at least two vessels, which operate alternately. A portion of the purified product from the operating vessel is directed to the other vessel and there used to remove accumulated contaminants from that vessel's zeolite. The process thus provides self-regeneration, in that regeneration of one vessel occurs while the other vessel decontaminates contaminated fluid carbon dioxide, so that use of the two can be alternated for substantially continual production of purified fluid carbon dioxide. The invention provides purified fluid carbon dioxide used in manufacture of such products as high purity electronic, optical, prosthetic or similar products or polymers or pharmaceuticals or in beverages.