Only 36% Full: Allegiant Air's 11 Emptiest Routes Revealed [See Full List & Map]

Allegiant Air is an ultra-low-cost carrier that focuses entirely on leisure markets, all of which are domestic. In September, OAG data show that the airline is the United States' tenth-largest domestic operator for flights. However, when seats for sale are considered, its higher-capacity Airbus A319s and A320s andBoeing 737 MAX 8s means it jumps to eighth place.