[3] It is a major constituent of fuming sulfuric acid, oleum, and this is how most chemists encounter it.

As confirmed by X-ray crystallography, the molecule consists of a pair of SO2(OH) groups joined by an oxide.

The mutual electron-withdrawing effects of each sulfuric acid unit on its neighbour causes a marked increase in acidity.

There are salts of disulfuric acid, commonly called pyrosulfates, e.g. potassium pyrosulfate.

There are other related acids with the general formula H2O·(SO3)x though none can be isolated.