The ''S''sand Reservoir B CO/sub 2/ pilot was designed to demonstrate the feasibility of a downward CO/sub 2/ displacement in a steeply dipping, high temperature and high pressure Gulf Coast reservoir. Research results show that CO/sub 2/ injection is not a miscible process at the S Sand Reservoir B (SRB) conditions but a CO/sub 2/-crude oil vaporization process. Vaporization means that the CO/sub 2/ strips and replaces hydrocarbon components from the crude. The stripping is enhanced with repeated contacts with fresh CO/sub 2/. Results of experiments indicate that CO/sub 2/ diluted with five to ten percent of plant gas (primarily methane) would result in a miscible-like displacement process. It also appears that based on slim tube experiments alone, undiluted CO/sub 2/ might be the most efficient material for the SRB field test. Under SRB reservoir conditions, CO/sub 2/ not diluted with light hydrocarbons is more dense than the reservoir oil. Fortunately, process mechanisms can work to the benefit of displacement stability. Upon mixing SRB oil and CO/sub 2/, two phases are formed. The CO/sub 2/ rich vapor phase is less dense than the liquid phase. Based on a zero dimensional analysis and the phase behavior study results, the vertical displacement by CO/sub 2/PG or CO/sub 2/ alone should be gravity stable at the expected flood conditions. A mixture of five percent by volume of plant gas and 95 percent CO/sub 2/ is the recommended injection system for this field test. This dilution should allow gravity forces to augment the vaporization process.