A series of pilot-scale tests were conducted to determine the effects of various parameters on the densification of refuse derived fuel (RDF). The experiments included a series of bench-scale experiments involving a single die arrangement, as well as larger-scale studies in which a commercial pellet mill was used. The bench-scale tests (tests in which the pellets were individually formed), were conducted both to provide data needed for an analysis of the basis dynamics of pellet formation and as an aid in the interpretation of results obtained with the pellet mill. The energy required to overcome die friction was studied independently of the energy consumed in material deformation and compression. By so doing, it became possible to determine the specific effects of die length, diameter, and taper. The results also suggested explanations for the excessive die wear, and for the decreasing energy requirements for increasing the mass throughput observed in commercial pellet mills.