How many voices do most fugues use?

Most fugues are written in three or four voices. While the number of parts in a fugue is flexible, three or four voices are the most common configurations. It is important to note, however, that not all of these voices are necessarily used at every moment; for instance, episodes often proceed in only two voices.1

While two-voice fugues are rare and compositions featuring five, six, or seven parts are possible, they are considered uncommon.2