Column density ratios of selected O-COMs with respect to methanol in different astronomical objects (see references in Sect. 5.4). Species are divided into three groups with different atomic mass units (amu); those in parentheses are only shown for the degenerate detections in the comet 67P/C-G by the ROSINA mass spectrometer, and they have not been detected separately in other sources. The column densities of the species with the same atomic mass units have been added together. The data of IRS 48 are shown as upper limits due to the possible underestimation of the column density of methanol.