Core flood experiments on gas injection behavior have been conducted for one of the Iranian oil fields. Different gas injection experiments in horizontal and vertical situations are designed to study the effects of type of injected fluid and gravity force on oil recovery. A sand pack from the sands of Asmari formation of one of the Iranian oil fields is prepared and is saturated with the live oil of that field. To study the effect of gravity force, methane is then injected into the prepared sand pack in the horizontal and vertical positions. The results show that a vertical injection has a stronger effect on oil recovery due to gravity force effects. Then different gases, including nitrogen, methane, and carbon dioxide, are vertically injected in the sand pack. The maximum recovery is obtained for methane injection. When CO 2 is injected some signs indicate that asphaltene is precipitated.