Hollow fiber membranes are popular as they have a high specific membrane area. To take advantage of this, it is necessary to pack the fibers into closely packed bundles. The fibers in different positions in the bundle behave differently as they are exposed to different hydrodynamic conditions. In this paper, a 'model' bundle of 9 fibers was tested in a setup which provides flow measurement from individual fibers and the same suction pressure in each fiber. The parameters studied were packing density, cross flow velocity, feed concentration and bubbling. It was found that a low cross flow velocities, high pressures and high feed concentrations, the surrounded (center) fiber performed very poorly compared to the fibers at the corner and the sides. Under these conditions, the overall performance of the bundle was much worse that of a single fiber.