- Ohio Valley Tissue and Skin Center
- Ohio Veterinary Medical Association
- OhioHealth Berger Hospital
- OhioHealth Mansfield Hospital
- OhioHealth Marion General Hospital
- Ohiohealth O'Bleness Hospital
- OhioHealth Riverside Methodist Hospital
- OhioHealth Southeastern Medical
- Ohlone College
- Oki Data Americas, Inc.
- Oklahoma Association of Career and Technology Education
- Oklahoma Children's Hospital OU Health
- Oklahoma City
- Oklahoma City Convention and Visitors Bureau
- Oklahoma City Housing Authority
- Oklahoma City VA Health Care System
- Oklahoma Heart Hospital North
- Oklahoma Heart Hospital South
- Oklahoma Hospital Association
- Oklahoma Nurses Association
- Oklahoma Primary Care Association
- Oklahoma Public Employees Association
- Oklahoma Society of Association Executives
- Oklahoma State Orthopaedic Society
- Oklahoma State University Medical Center
- Oklahoma Surgical Hospital
- Oklahoma Transplant Institute
- Oklahoma University Medical Center
- Olathe Medical Center
- Old Dominion Electric Cooperative
- Olean General Hospital
- Olinger Crown Hill Mortuary and Cemetery
- Olinger Mortuary and Cemetery
- Olive Garden
- Olive View-UCLA Medical Center
- Oliver Williams and Davis
- Ollie Steele Burden Manor
- Olmsted Medical Center
- Olympia Medical Center
- Omaha Public Power District
- Omaha Standard, Inc.
- OMARA Organization
- Omega Health Care
- OMMI - Means
- Omni Corpus Christi Hotel
- Omni Hotels
- Omni Indianapolis North Hotel,
- Omni Shoreham Hotel
- Omni Sonics
- Omnicare, Inc.