The invention relates to a method for resolving a hydrocarbon-rich, nitrogen-containing feed fraction (1, 1′), preferably natural gas, is described, wherein the feed fraction (1, 1′) is separated by rectification (T1, T2) into a nitrogen-enriched fraction (5) and a hydrocarbon-rich, nitrogen-depleted fraction (10), and wherein the separation by rectification proceeds in a rectification column consisting of a preseparation column (T1) and a main separation column (T2). A liquid fraction (6) is taken off from the main separation column (T2) above the feed-in site(s) of the fraction (7, 7′, 7″) that is taken off from the preseparation column (T1) and fed to the main separation column (T2), and the liquid fraction (6) is applied to the preseparation column (T1) as reflux.