A gas chromatograph for analyzing natural gas, with a first separation column (6). A first detector (7) is provided following the first separation column, the first separation column and the first detector operable to separate or detect propane and higher hydrocarbons. A second separation column (8) and a second detector (9) following it are provided to separate or detect carbon dioxide and ethane. A third separation column (10) and a third detector (11) following it are provided to separate or detect nitrogen and methane. A controllable changeover device (12) is provided between the second separation column (8) and the third separation column (10) to discharge eluates following methane. The first, second and third separation columns (6, 8, 10) and the first, second and third detectors (7, 9, 11) are connected in series. At least the first and the second detectors (7, 9) are operable to detect a mixture of substances flowing through them in a non-destructive manner.