Heavy oil or bitumen is extracted and removed from underground oil bearing formations having low permeability such as tar sands by injection of hot hydrocarbon solvent vapor into a single well hole at a pressure not substantially exceeding the pressure in the formation to effectively heat and extract the bitumen. The hot solvent vapor is passed downwardly through an annular passage of concentric piping place in the well bore and is injected out through upper performations in the casing and into the formation. The hot solvent vapor condenses in the formation and drains along with recovered oil through lower perforations back into the bottom end of the inner pipe, from which the product oil and solvent mixture is pumped to above ground. The solvent is partially reclaimed from the oil product by distillation means and the solvent friction is reheated and reinjected into the well bore for further use.
The solvent used should be matched to the characteristics of the bitumen in the tar sands formation for most effective recovery of bitumen, and contains substantially aromatic compounds. As more bitumen is dissolved and removed from the formation, the injection and drainage perforations in the casing are spread further apart vertically so as to cause the solvent to penetrate the formation more effectively and dissolve bitumen further away from the bore hole.