OAA
- Fédération Internationale de l'Automobile
- ICAO
- Oakwood Adventist Academy
- Oceania Athletic Association
- Office of the Administrative Assistant to the Secretary of the Army
- Ohio Achievement Assessment
- Old Achimotans Association
- Older Americans Act
- One Ayala Avenue
- Ontario Association of Architects
- Open Agent Architecture
- Open Automotive Alliance
- Open adoption
- Optically active additive
- Optometrists Association Australia
- Orlando Apopka Airport
- Oxaloacetic acid
- Oxford Aviation Academy
- Ozark Adventist Academy