The effect of prime fluid flow orientation on non-Brownian oil-drop steady-state coalescence in a high-porosity bed was investigated. This effect was analyzed via effluent oil concentration and critical velocity. Three fluid flow orientations were examined, namely, horizontal, vertical up, and vertical down, over a wide range of bed properties and working velocities, as well as three bed lengths. On the basis of the effluent oil concentration, the effect of flow orientation is dominantly determined by fluid velocity. It was concluded that the horizontal flow is most effective for a steady-state bed coalescer, over all working conditions.