The sweep efficiency of a steam drive process is improved and steam override reduced significantly if steam is injected into a formation until channeling has begun, after which steam injection is terminated and a slug of a thermally stable diverting fluid comprising a high molecular weight hydrocarbon within the temperature range of 500.degree. to 1000.degree. F. is injected into the steam-swept zone and allowed to cool until the diverting fluid has increased in viscosity to a value greater than the in place oil thereby creating a highly immobile slug in the steam-swept zone. Thereafter, injection of steam is continued and oil recovered. Multiple cycles of steam injection and rejection of slugs of diverting fluid may be repeated to improve sweep efficiency depending upon the vertical thickness of the formation.