The resistivity of a filled polymer system has been evaluated as a function of the filler concentration. The system is based on a model which takes into account non-ohmic conduction phenomena such as the Schottky effect, the Poole-Frenkel effect, space charge limited conduction and quantum mechanical tunneling. It has been shown that most of the reported data on polymers loaded with conducting carbon blacks or other fillers can be explained on the basis of this model without invoking the formation of contacts between the particles. The internal conduction processes responsible for the charge transport in these systems are also delineated.