Toner transfer efficiency in electrophotography and the resulting image quality are influenced by the resistivity of the substrate. Resistivity measurements are, however, often made using electric fields that are lower than those used in the transfer of toner in electrophotography. The dependence of surface and volume resistivity on electric field strength, including fields similar to those utilized in the toner transfer of electrophotographic printers, has been studied. Resistivities of paper samples with differences in grammage, filler content, and calendering were evaluated utilizing electrodes with a geometry in accordance with the ASTM D257 (volume resistivity) and raker-type electrodes (surface resistivity) applying electric fields of between 10² and 10⁵ V/cm. The surface resistivity and especially the volume resistivity of paper were found to be strongly dependent on the electric field strength, the characteristics of this dependence being influenced by paper properties. The study of the field dependence further indicated that the Poole-Frenkel type of hopping drift of ions could be applied to conduction in paper, although the electric field dependence was overlapped by paper compression effects. Shottky's model was considered also, but it seems that the role of contact effects is small.