The major challenge which limits the application of inorganic perovskite multiferroics is the presence of high conductivity giving rise to extrinsic factors which suppress intrinsic ferroelectric response. Therefore, it is vital to identify, control and understand conductivity effects in these perovskite oxides. For this purpose, the electrical and dielectric response of well-known multiferroic, BiFeO3 (BFO), has been extensively studied. In the present study role of oxygen, vacancies have been investigated clearly and intentionally controlling the formation of space charges via a variety of isovalent and aliovalent substitutions. Based on the activation energies, calculated for the three identified thermal activated processes, a potential well diagram is proposed.