The lowest pressure at which CO/sub 2/ can develop miscibility with a particular reservoir oil is termed the ''minimum miscibility pressure''(MMP). There are two major factors which determine the CO/sub 2/ MMP, reservoir temperature and crude oil composition. The purpose of this investigation was to use compositional data to suggest how the compositional changes which accompany a CO/sub 2/ oil displacement affect the observed recovery efficiency. The experimental approach was to perform sandpack displacements of dead Brookhaven crude oil at a variety of temperatures and pressures (Part I), and to perform corefloods using CO/sub 2/ with synthetic or natural reservoir oil systems (Part II). The sandpack results provide compositional proof that for a given temperature, increasing pressure affects greater oil recovery. Compositional analyses of samples from displacements performed at lower pressures indicate that the major components extracted into the CO/sub 2/-rich phase are in the C/sub 9/ to C/sub 12/ range. As the run pressure is increased, the ability of CO/sub 2/ to extract heavier hydrocarbons improves to provide greater oil recoveries. To determine whether the improvement in hydrocarbon extraction observed in static PVT measurements would translate into higher oil recoveries in CO/sub 2/ displacement tests, tertiary corefloods were performed using synthetic oils. The coreflood results show that the oil displacement efficiency for CO/sub 2/ flooding is improved by increasing the aromatic content of the oil. Another series of corefloods was initiated to examine the gravity stable displacement process. Ongoing experiments are quantitating the incremental oil recovered with injection rate reduction for a reservoir amenable to gravity stable flooding. Progress to date is presented. 25 refs., 24 figs., 33 tabs.