Photosensitized and cation radical-catalysed electron-transfer oxygenations of 3-phenyl-1,1,2,2-tetramesityl-1,2-digermetene 1 affords the corresponding 1,2,3,6-dioxadigermine 2 as a dioxygen insertion product into a Ge-Ge sigma-bond in moderate yields together with 1,2,5-oxadigermolene 3.