Abstract It is well known that charge carrier mobilities μ in molecularly doped polymers (MDP) determined by transient photoconductivity experiments depend on three variables, the temperature T, the mean distance between dopant molecules ρ, and the electric field E. Recently introduced deconvolution procedures have made possible the first systematic determination of the dependence of μ on T, ρ, and E. This determination led to the suggestion that the T and ρ dependencies are consistent with small polaron theory. However, the electric field dependence of μ remains unexplained. In this paper we present an in-depth study of the electric field dependence of charge carrier mobilities in MDP.