Steam injection in naturally fractured formations has been drawing considerable interest for more than three decades. It is believed that the steam heats the rock, which then undergoes a thermally induced wettability reversal. Hot water can then spontaneously imbibe into the water wet rock matrix, resulting in favorable oil recoveries. In this study, the applicability of steam injection in an oil wet undeveloped Iranian extra-heavy oil fractured carbonate reservoir is discussed. A geological model calibrated with results of a handmade model was used to study the optimum operating conditions under continuous steam injection. It was observed that under this operating strategy in which the main oil production mechanism is heat transfer, steam injection rate and existence of layers which are open to flow, injection and production pattern are directly related to success of the process and because of high viscosity of oil at the reservoir temperature its influences on final recovery is negligible. Initial pressure of the undertaken reservoir is 927 psi at 1700 ft depth. The gravity of the oil is 7.24 °API with viscosity of about 2700 cp at reservoir temperature. This field is a highly fractured carbonate reservoir with 3.6 billion barrel estimated oil in place. It was further observed that during 50 years which this reservoir has been undertaken to study under discussed recently found strategy, crude oil production reaches to more than 900 barrels per day.