Abstract Slumping and rolling beds have been studied extensively in a continuous pilot kiln and batch rotary cylinders. Solids investigated include nickel oxide pellets, limestone, sand, and gravel. The effect of variables such as rotational speed, bed depth, cylinder diameter, particle size, and particle shape on bed motion has been determined. For a given material, the different modes of bed motion can be delineated conveniently on a Bed Behavior Diagram which is a plot of bed depthvs rotational speed. The scaling of bed behavior with respect to particle size and cylinder diameter requires similarity of Froude number modified by(D/d p)1/2, and pct fill. Measurements of key variables characterizing slumping and rolling beds have also been made.