Abstract: There is disclosed a method of recovering viscous oil from a subterranean viscous oil-containing formation separated into at least one upper and at least one lower zone by a horizontal layer having lower vertical permeability than the rest of the reservoir. The method comprises injecting steam into the lower zone until steam breakthrough occurs at the production well; subsequently injecting steam into both the upper and the lower zones; and, continuing to inject steam into both zones and recovering fluids, including oil from the production well.