The possible deformation behavior of spheres in a compact has been both theoretically analyzed and experimentally verified. The change in contact area radius a relative to the particle radius R has been related to the bulk density and bulk strain for four possible modes of packing: simple cubic (Z=6), orthorhombic (Z=8), rhombohedral (Z=12), and body-centered cubic (Z=8). An equation relating the above parameters can be represented by D−D0=32D0(a/R)2 for different types of packings, D and D0 being densities at any a/R and a/R=0, respectively. It has been shown experimentally by deforming lead spheres at room temperature, 50° and 100°C in a cylindrical die, that the over-all deformation is similar to that of the orthorhombically packed monosized spheres. A change in the coordination number Z during the deformation process was also observed and may account for the deviation from the theoretically predicted values. Similar experiments using sapphire spheres were carried out in the temperature range 1570°–1700°C, and the results showed that the deformation behavior was very similar to that of the lead spheres.