The influence of viscosity and polarity of the rubber matrix and the type and content of extender oils on the carbon black dispersion has been characterized using the online electrical conductivity measurement. The experimental results have been discussed on the basis of the infiltration model proposed by Manas-Zloczower. A corresponding change of the online conductivity and the rubber infiltration and carbon black dispersion has been observed. The infiltration rate increases with increasing polarity and decreasing viscosity of the rubber matrix. However, the matrix polarity shows a stronger effect than the matrix viscosity. The oil addition influences the infiltration process by changing the matrix viscosity and the filler-matrix interaction as well as the shear force. Oil addition affects the carbon black dispersion in the non-polar rubber more effective than in the polar rubber, and in the non-polar rubber the polar oil shows a stronger effect than the non-polar oil.