required will be such as to provide a vapor volume equal to the liquid volume of the bitumens being recovered the furthest point of approach of the vapors into the tar sand formation is indicated by a wavy line 16 the hot solvent vapors are introduced to the tar sand formation at a rate such as to exert a small preselected back pressure preferably a few pounds per square inch gauge or less thus a sufficient superheat to maintain a small temperature gradient between the point of injection of the solvent vapors into the formation and the interface between the leached and unleached portions thereof is provided in this manner any heat losses such as may result from the presence of foreign bodies shale breaks for example are accommodated the temperature of the leached portion of the formation is maintained above the condensation point and further leaching of the residual tar is avoided when all the bitumen is extracted from a true tar sand the residual sand has no inherent strength and crumbles some of the so called 34 tar sand 34 formations are actually sandstone formations similar to an oil bearing sand formation this rock type is not as readily extracted by the vapor solvent method tests of this method on plugs cored from asphalt rocks gave a maximum recovery of only 30 50 with any of the usual solvents for efficient bitumen recovery by the present method a plurality of closely spaced wells is drilled into the tar sand formation the spacing selected will depend somewhat on the depth and thickness of the formation but on the average will be.