One of the important mechanisms in the primary production of heavy oil reservoirs under solution gas drive is the foamy oil flow effect. This form of flow occurs only under certain combinations of capillary, viscous, and gravity forces. Several studies have been carried out to examine this effect on the recovery process, but it remains poorly understood and difficult to model. The objective of this study was to examine the roles of capillary, viscous, and gravity forces in foamy oil flow. Primary depletion experiments were conducted in a 2 in long sand pack holder to measure the oil and gas production at different depletion rates. The effect of gravitational forces was investigated by comparing the experiments conducted in horizontal and vertical orientations of the 2 in long sand pack. In the vertical orientation, the solution gas drive performance was evaluated with production from the bottom end of the sand pack, as well as with production from the top end. The experimental results are presented in terms of the oil and gas production behaviour affected by the capillary number and gravity forces. The results indicate that the gravity forces do not significantly influence the ultimate oil recovery when the oil is produced under foamy oil flow. Even at the lowest depletion rate used in these tests, when the oil flow and gravity are in the same direction, gravity segregation of gas did not improve the oil recovery significantly. Recovery efficiency and the critical gas saturation at which free gas flow starts are primarily dependent on the capillary number.