A system and method for producing bitumen or heavy oil from a clastic or carbonate reservoir. The mobility of the bitumen or heavy oil is increased by conductive heating to reduce the viscosity. The bitumen or heavy oil is heated to temperatures below the thermal cracking temperature of the bitumen or heavy oil. As the bitumen or heavy oil is produced, evolved gases or evaporated connate water or both form a gas chamber which acts to replace the volume of the produced fluid required for the gravity drainage process.