NOVELTY - Conditioning a portion of a gas stream comprising at least methane and C2+ hydrocarbons, comprises: withdrawing the portion from the high-pressure gas stream (200); providing a membrane unit having e.g. a feed side, and containing a membrane selective for methane over C2+ hydrocarbons; passing the portion as a feed stream across the feed side; withdrawing a membrane residue stream (206) from the residue side; withdrawing a membrane permeate stream (207) from the permeate side; and routing the membrane permeate stream as a portion of a fuel gas stream to a fuel user (208).    USE - The process is useful: for conditioning a portion of a gas stream, which is useful to a fuel user such as a gas engine for driving a compressor (all claimed); and in turbine-driven compressors and the gas field or the gas processing plant.    ADVANTAGE - The process easily provides an improved conditioned gas stream with less energy consumption and under less heating conditions, thus providing reduced emissions from the engines with less energy consumption, hence the stream avoids polluting the environment.    DETAILED DESCRIPTION - Conditioning a portion of a gas stream comprising at least methane and C2+ hydrocarbons, comprises: withdrawing the portion from the high-pressure gas stream (200); providing a membrane unit having a feed side, a permeate side and a residue side, and containing a membrane selective for methane over C2+ hydrocarbons; passing the portion as a feed stream across the feed side under conditions in which transmembrane permeation occurs; withdrawing a membrane residue stream (206) from the residue side; withdrawing a membrane permeate stream (207) from the permeate side, where the permeate stream is enriched in methane and depleted in C2+ hydrocarbons compared with the filtered stream; and routing the membrane permeate stream as a portion of a fuel gas stream to a fuel user (208).    DESCRIPTION OF DRAWING(S) - The figure shows a flow chart of a process for conditioning a portion of a gas stream.    High pressure gas stream (200)    Pre-treatment step (202)    Membrane residue stream (206)    Membrane permeate stream (207)    Fuel user. (208)