Gaseous and liquid products discharged from the outlet of an in-situ retort for the retorting of oil shale are delivered into an underground separating chamber located substantially at the level of the bottom of the retort. The lower portion of the separating chamber is divided by a weir into a first sump adjacent the inlet end of the separating chamber and a second sump adjacent the outlet end of the separating chamber. Oil and water separate in the first sump and the oil overflows the weir into the second sump. Water is withdrawn at a level below the oil in the first sump and pumped to the surface. Oil is withdrawn from the second sump and pumped to the surface separately from the water.