A system for heating at least a part of a subsurface hydro carbonaceous earth formation forms a borehole into or adjacent to the formation, places elongated coaxial inner and outer conductors into the borehole with the inner and outer conductors electrically connected to each other at a depth below the top of the formation, and connects an AC power source to at least the outer conductor to produce heat in at least one of the conductors. The AC output has a controlled frequency, and the outer conductor comprises a standard oil well component made of a ferromagnetic material that conducts current from the AC power source in only a surface region of the conductor due to the skin effect phenomenon. More heat is dissipated from portions of the conductor that is within the depth range of the formation than from other portions of the conductor. The inner conductor may optionally be a standard tubular oil well component made of a ferromagnetic material that conducts current from the AC power source in only a surface region of the conductor due to the skin effect phenomenon.