A first conductor is positioned in the substantially horizontal or inclined portion of a first wellbore. The first conductor includes electrically conductive material. A portion of the first conductor positioned in the first wellbore includes copper coupled to the electrically conductive material. The copper tapers from a larger thickness at a first end of the portion to a smaller thickness at a second end of the portion. A power supply coupled to the first conductor electrically excites the electrically conductive materials of the first conductor such that current flows between the electrically conductive materials in the first conductor, through at least a portion of the formation, to a second conductor located in the hydrocarbon containing layer in the formation, and the current resistively heats at least a portion of the formation between the two conductors.