Thermal methods for enhanced oil recovery account for the large share of the world's production. Steam flooding is one of the oldest commercial methods to enhance the heavy oil recovery. In due respects, experiments of steam injection into a sand pack were performed to study the recovery of heavy oil (API<20) and a lighter oil (API>20) of Iranian field. Two different porosity of sand pack were used and the experiments were conducted with four different types of heavy oil, with different API, to study their effect on recovery. An experimental setup was designed and used to inject the steam into the sand pack. Using different pressures at each experimental run, results show that there is an optimum pressure, which is the characteristic of each reservoir and must be determined by field experiments. The rate of injected steam has an important effect on recovery and an optimum rate exists for ultimate recovery. Steam injection is more effective for heavy oil reservoirs, as for light oil reservoirs; there is the risk of fingering which results in production of steam without sufficient oil production. Even though, in literature, some authors have indicated that the steam injection could be used for the lighter oil reservoirs (API~ 24 or more) but based on the conducted experiments it is proposed to take more care.