A variable current density electrode system for in vivo electroporation, comprising: a geometric planar ring electrode that is electrically isolatable into two electrically conductive halves; an elongate needle electrode having a proximal end and a distal end, wherein the elongate needle electrode includes: an electrically non-conductive portion located along a proximal region of the elongate needle electrode and being electrically non-conductive, and a distal electrically conductive portion, wherein the elongate needle electrode is tubular and capable of channeling an injection fluid from a reservoir, wherein a surface area ratio between the ring electrode and the elongate needle electrode is in a range between 1000: 1 and 5: 1; and electronic circuitry connected to both the elongate needle electrode and the ring electrode for delivering an electroporative pulse to cells of a body tissue, wherein during the electroporative pulse the electric current density in the body tissue at or near the elongate needle electrode is higher than electric current density in the body tissue at or near the ring electrode, characterized in that the elongate needle electrode defines apertures that are disposed along a length of the conductive portion and around a circumference of the conductive portion, wherein the plurality of apertures are configured to provide even distribution of the injection fluid over the length of the conductive portion. a geometric planar ring electrode that is electrically isolatable into two electrically conductive halves; an elongate needle electrode having a proximal end and a distal end, wherein the elongate needle electrode includes: an electrically non-conductive portion located along a proximal region of the elongate needle electrode and being electrically non-conductive, and a distal electrically conductive portion, wherein the elongate needle electrode is tubular and capable of channeling an injection fluid from a reservoir, wherein a surface area ratio between the ring electrode and the elongate needle electrode is in a range between 1000: 1 and 5: 1; and an electrically non-conductive portion located along a proximal region of the elongate needle electrode and being electrically non-conductive, and a distal electrically conductive portion, wherein the elongate needle electrode is tubular and capable of channeling an injection fluid from a reservoir, wherein a surface area ratio between the ring electrode and the elongate needle electrode is in a range between 1000: 1 and 5: 1; and electronic circuitry connected to both the elongate needle electrode and the ring electrode for delivering an electroporative pulse to cells of a body tissue, wherein during the electroporative pulse the electric current density in the body tissue at or near the elongate needle electrode is higher than electric current density in the body tissue at or near the ring electrode, characterized in that the elongate needle electrode defines apertures that are disposed along a length of the conductive portion and around a circumference of the conductive portion, wherein the plurality of apertures are configured to provide even distribution of the injection fluid over the length of the conductive portion.