“…Many investigators have reported both experimental and theoretical results for the effects of gravity and viscosity on the stability of miscible displacements (Hill, 1952;Perrine, 1961 and1963;Dumore, 1964;Tan andHomsy, 1987 and1988;Homsy, 1987;Hickernell and Yortsos, 1986;Manickam and Homsy, 1995) and immiscible displacements (Engelberts and Klinkenberg, 1951;Chuoke et al, 1959;Terwilliger et al, 1951;Sheldon et al, 1959;Fayers and Sheldon, 1959;Raghavan and Marsden, 1971;Nayfeh, 1972;Peters and Flock, 1981;Glass and Yarrington, 1996;Stephen et al, 2001;Meheust et al, 2002;Ould-Amer and Chikh, 2003;Riaz and Tchelepi, 2004). Many investigators have reported both experimental and theoretical results for the effects of gravity and viscosity on the stability of miscible displacements (Hill, 1952;Perrine, 1961 and1963;Dumore, 1964;Tan andHomsy, 1987 and1988;Homsy, 1987;Hickernell and Yortsos, 1986;Manickam and Homsy, 1995) and immiscible displacements (Engelberts and Klinkenberg, 1951;Chuoke et al, 1959;Terwilliger et al, 1951;Sheldon et al, 1959;Fayers and Sheldon, 1959;Raghavan and Marsden, 1971;…”