NOVELTY - Treating a natural gas stream involves passing the gas stream through a membrane element comprising a perforated non-permeate pipe (35) sharing a central longitudinal axis (37) of the membrane element; and several hollow fibers (21) arranged about the perforated non-permeate pipe. The hollow fibers include a first and second hollow fiber type, where the first and second hollow fiber types exhibit at least one different performance characteristic from the other.    USE - For treating a natural gas stream to remove acid gas such as carbon dioxide and hydrogen sulfide (claimed) and other components from the natural gas stream.    ADVANTAGE - The membrane element has requisite performance characteristics for improved gas separation even as the gas volume and composition change as the gas travels through the membrane. The membrane fibers have different characteristics for reducing the number of membrane elements required for gas separation and thus improves gas separation performance due to changing gas composition because of permeation as the gas travels through the membrane element. The method removes acid gas and other components from the natural gas stream so that the gas can be usable for fuel. The single membrane filter element effectively accomplishes a range of separation from high carbon dioxide to low carbon dioxide (or vice versa) and the filter element can be optimized to at least two distinct separation functions including carbon dioxide and hydrogen sulfide separation or carbon dioxide and hydrocarbon dew-pointing. The membrane filter element has improved membrane efficiency and a better overall separation capacity and it simplifies process control by reducing the number of filtering stages that require monitoring and eliminating the need for plant operators to rebalance flow rates between multiple stages of membrane filter elements or to change the relative loading between these stages. The membrane filter element has increased flexibility in accommodating changes in inlet gas composition over time and it creates more resistance to bypass or gas channeling and, therefore, eliminates the need for internal baffles or other gas distribution mechanisms. Because of the increased fiber bundle depth, the membrane filter element can replace two stages of smaller conventional membranes. The larger bundle depth thus enables the use of multiple fiber types in a single membrane element and provides separation performance similar to that which previously required gas to pass through at least two membranes in series. Carbon dioxide (CO2) is selectively separated within the membrane element as the flowing mixed CO2/hydrocarbon gas comes in contact with the fibers.    DESCRIPTION OF DRAWING(S) - The figures show a graphical depiction of the hollow fibers and an end view of the multiple fiber membrane filter element.    Hollow fiber (21)    First circumferential zone of fibers (31)    Second circumferential zone of fibers (33)    Perforated non-permeate pipe (35)    Gas inlet or feed side of multiple fiber membrane element (41)    Outlet or non-permeate side of multiple fiber membrane element (43)