Abstract: An improvement is provided in an in situ steamflooding process for recovering oil from a subterranean, heavy oil-containing reservoir. An organic sulfonate surfactant, for example a petroleum sulfonate surfactant, is injected with the steam into the reservoir. The steam-surfactant injection stream is introduced to the reservoir at a temperature in the range of about 180.degree. C. to 260.degree. C. The process may be practised in a single well or multi-well pattern using any of a continuous steam drive, steam soak or cyclic steam recovery program. A substantial increase in oil recovery is achieved by this process, as compared to a steam-only injection scheme.