A model has been formulated for estimating the oil production during the mature phase of a steam-injection process. This model assumes that complete steam overlay has occurred and that subsequent gravity drainage of oil is accelerated because of the viscosity reduction in the heated-oil phase. The predicted oil-production rate declines approximately linearly at early times, depending on the initial oil level in the reservoir and at a gradually decreasing rate toward zero at long times. The model shows good agreement with various field cases.