Abstract: There is obvious pattern for oil/water distributiaon in the Carboniferous volcanic reserviors of Shixi oil-field. The specific gravity of crude oil increase towards the north and it is not controlled by structures. It is different in east and west blocks for characteristics of formation water. Water with low salinity is distributed in the west block and the gradient of ionic concentration is from south t0 north; and water with high salinity is distributed in the east block and the gradient of ionic concentration is from west to east. It is suggested that migrati0n direction of oil and formation water was from south to north and the fault in the middle of the reservi0r was a main factor in influencing distribution of formation water and hydrocarbon abundance.