The mobilities of positive charge carriers in polyaniline films measured as a function of oxidation level are discussed with the help of in-situ ESR measurements. Three different processes are found to occur over oxidation levels ranging from 0.1 to 43%. An initial decrease of mobility is followed by a small hump at oxidation levels up to 7%. This mobility change is ascribed to a change in conformation from coil to expanded coil. which is supported by optical absorption spectra. The rise in mobility from an oxidation window of 7 to 36% can be interpreted well in the framework of a polaron lattice model. ESR data provide strong evidence for the transformation between Curie and Pauli spins. The decrease in the mobility above the 36% oxidation level is accounted for in terms of a transition from the emeraldine salt to the base form.