It has been found that appreciable carbon black flocculation can occur in filled rubber stocks during storage or vulcanization in the absence of shear. The kinetics of this flocculation process were studied by means of low strain dynamic mechanical property and electrical conductivity measurements. The results showed the rate of flocculation to be governed by the type and concentration of carbon black, polymer macrostructure, mixing history, and annealing temperature. A mechanism responsible for the formation of this carbon black network structure was proposed and the resulting changes in the physical properties of vulcanizates prepared from these rubber compounds were elucidated.