Following the guidelines at Wikipedia:WikiProject Opera#Categories, all of the Gilbert and Sullivan operas are categorized as follows:
The operas that Arthur Sullivan wrote with other librettists, except for Ivanhoe, are categorized as follows:
Ivanhoe is not in Category:English comic operas, but otherwise it is categorized like any other Sullivan opera.
The operas that W. S. Gilbert wrote with other composers are categorized as follows:
In addition, each opera by Gilbert and/or Sullivan is in the appropriate sub-category of Category:Operas by year. For instance The Mikado is in Category:1885 operas.
In each of the above scenarios, the minimum categories are listed. Some works also fall into additional categories. See The Pirates of Penzance and The Emerald Isle for examples.