Heavy or viscous oils may be recovered from subterranean deposits by one or more wells each of which is provided with at least two separate communication means from the surface of the earth, one in fluid communication with the upper part of the formation and the other well being in fluid communication with the lower part of the formation, each of said communication means being completed so as to permit injection of steam or mixtures of steam and other materials into the formation and production of heated viscous petroleum therefrom. The oil recovery process comprises several separate phases of operation. In the first, steam is injected into the formation using both communication means simultaneously for a period of time followed by a soak period if desired, followed by production of heated oil from both parts of the formation using both communication means simultaneously. In the second phase, steam is injected into only one of the communication means, which may be the one in communication with either the top or bottom part of the formation, and oil production is taken from the other communication means. This is followed by a reversal of injection-production sequences, the process effectively pressure pulsing the formation to improve the distance into the formation that the push-pull steam injection process is effective.