Reducing viscosity of oil for production from a hydrocarbon containing formation

A method for treating a hydrocarbon containing formation (104), comprises applying electrical current to one or more electrical conductors (106) located in an opening in the formation to provide an electrically resistive heat output; allowing the heat to transfer from the electrical conductors to a part of the formation containing hydrocarbons so that a viscosity of hydrocarbons in the part and at or near the opening in the formation is reduced; providing gas at one or more locations in the opening to reduce the density of the hydrocarbons so that the hydrocarbons are lifted in the opening towards the surface of the formation by the formation pressure; and producing the hydrocarbons through the opening. At least one of the electrical conductors comprises an electrically resistive ferromagnetic material and provides a reduced heat above or near a Curie temperature of the ferromagnetic material, and the produced hydrocarbons have an API gravity of 20 degrees or less.