NOVELTY - Providing a method and apparatus that lowers the vapor traffic through the higher pressure rectification column and thereby makes it possible to keep down the diameter of the column.    USE - For rejecting nitrogen from a feed gas stream.    ADVANTAGE - The inventive method keeps down the vapor traffic through the higher pressure rectification column, making it possible to keep down the diameter of this column. It provides reduced effective range of vapor loadings that both rectification columns of the first double rectification column have to face during their operating lifetime.    DETAILED DESCRIPTION - Rejection of nitrogen from a feed gas stream comprising methane and nitrogen (the mole fraction of nitrogen in the feed gas increases over a period of time) to form a methane product, comprises:    (a) cooling the feed gas stream in a main heat exchanger (4);    (b) rectifying the cooled feed gas stream in a double rectification column (12A), a lower pressure rectification column (16A) and a condenser-reboiler (18A) placing the higher pressure rectification column (14A) in heat exchange relationship with the lower pressure rectification column, at least part of the feed gas stream is expanded into the higher pressure rectification column, and the feed gas stream is partially liquefied upstream of the double rectification column; and    (c) operating a second double rectification column (12B) in parallel with the first double rectification column, but only at increased nitrogen mole fraction values of the feed gas stream.    An INDEPENDENT CLAIM is included for an apparatus for rejecting nitrogen from a feed gas stream as above, comprising a main heat exchanger for cooling the feed gas stream; a double rectification column for rectifying the feed gas stream, comprising a higher pressure rectification column, a lower pressure rectification column, and a condenser-reboiler; an expansion device downstream of the main heat exchanger communicating with the higher pressure rectification column; and a second double rectification column in parallel with the first double rectification column. The expansion device is arranged in such a way that it introduces a part of the feed gas stream into the higher pressure rectification column in liquid state.    DESCRIPTION OF DRAWING(S) - The figure shows is a schematic flow diagram of a nitrogen rejection plant.    Main heat exchanger (4)    Double rectification column (12A)    Second double rectification column (12B)    Higher pressure rectification column (14A)    Lower pressure rectification column (16A)    Condenser-reboiler (18A)