The inverse fluidization of unequal solid species of a binary-pair leads to the occurrence of their stratification along the height of the bed. This phenomenon depends upon the difference in the physical properties and the relative composition of the individual species comprising the binary-pair besides the fluid velocity. Packing models are used here to account for the observed volume-contraction owing to the mixing of unequal solid species. In view of stability considerations, the minimum bulk density condition is used to predict the composition of the upper-layer located below the distributor. Predictions are consistent with the observed stratification pattern reported in the literature. (C) 2010 Elsevier B.V. All rights reserved.