The effects of buoyancy forces on the displacement of one liquid by another in a consolidated porous medium have been investigated experimentally for the specific case in which the two liquids are completely miscible. In order to obtain a clear understanding of the favorable and unfavorable effects of buoyancy forces, experiments were carried out in three different flow modes, namely horizontal, vertical-downward and vertical-upward. As the effects of buoyancy forces are negligible for two-dimensional porous media in the horizontal flow mode, the results obtained in this mode were used as a reference for comparison with those obtained in the two vertical modes. The miscible system employed consisted of an aqueous glycerol solution and distilled water (dyed with methylene blue) as the displaced and displacing fluids respectively. Displacements using five different density ratios were studied, with the density ratio being varied by changing the concentration of the glycerol solution. The breakthrough time and fractional recovery of the displaced fluid were measured in each case and photographs of the unstable fingering patterns were taken for a wide range of injection flow rates. The results obtained indicate that the effects of buoyancy forces can be very significant, especially at low flow rates and/or at high density ratios. When the density of the displacing fluid is less than that of the displaced fluid (which was the case in the present work), buoyancy forces play a deleterious role in vertical-upward displacements since they tend to promote fingering and reduce breakthrough times, thereby producing low recoveries of the displaced phase. In contrast, under the same density conditions, buoyancy forces play a positive role in vertical-downward displacements since they then tend to stabilize the displacement process (i.e. reduce fingering), thereby producing increased breakthrough times and correspondingly high recoveries of the displaced phase. However, at high flow rates, the observed fingering patterns and recoveries are very similar for horizontal, vertical-downward, and vertical-upward displacements, since viscous forces are dominant under such conditions and buoyancy forces are insignificant.