Dispersion of carbon black in compounds for practical use is examined from three aspects; effects of carbon black loading, deformation characteristics of raw polymer, and chain scission during mixing. A threshold carbon black loading, above which efficiency of dispersion is greatly improved, is found to exist. It coincides with the percolation threshold of the filler and also with the loading where appreciable Payne effect becomes detectable. The findings suggest that dispersion in practical compounds proceeds most efficiently via elongation of agglomerates. The relations of dispersion with deformation characteristics of raw polymer and with the extent of scission in agglomerates also support the elongation-driven mechanism in dispersion of the filler loaded above its percolation threshold.