Abstract: A process and apparatus is described for use in the recovery of oil from natural oil-bearing formations such as tar sands by means of thermal energy causing the oil to gravity in the formation into an oil-receiving duct. Oil recovery in relation to installation and operating costs is improved by releasing heat into the formation at the site of the oil-receiving duct. For this purpose a composite heating and oil recovery string is used which is installed along the formation and comprises a tubular casing having oil-entry apertures and, internally of such casing, an oil-receiving duct and a passageway for the circulation of fluid heating medium.