S91 may refer to:
S91 (New York City bus), serving Staten Island "S91" (song), a 2023 song by Colombian singer Karol G Blériot-SPAD S.91, a French biplane fighter County Route S91 (Bergen County, New Jersey) Daihatsu Zebra (S91), a pickup truck and van , a submarine of the Royal Navy SIPA S.91, a French trainer aircraft