- Occupational safety and health
- Oil store
- Outdoor swimming pool
- Office furniture store
- Office
- Office space rental agency
- Outdoor furniture store
- Orthopedic clinic
- Optical wholesaler
- Orthodontist
- Office building
- Otolaryngologist
- Outdoor sports store
- Oil wholesaler
- Office equipment rental service
- Office equipment repair service
- Office supply store
- Obstetrician-gynecologist
- Ophthalmology clinic
- Oral surgeon