- Onslow Memorial Hospital
- Opelousas General Health System
- Open Door-BMH Health Center
- Open Works
- Operation Lifesaver Inc and National Support Center
- Operational Technologies Corporation
- Opnet
- Optical Gallery of Arizona
- Optical Laboratories Association
- Optima Products, Inc.
- Optimal Therapy Associates Services
- OptimuMedicine, LLC
- Options Unlimited, Inc.
- Optometrist
- Optometry Board
- OPUS Design Group
- Oquendo Velez S. Associados, Inc.
- Oracle
- Orange City Area Health System
- Orange Coast Association Of Realtors
- Orange County Association of Realtors
- Orange County Global Medical Center
- Orange County Government
- Orange County Health and Family Services Department
- Orange County Sheriff's Office
- Orange Ford Lincoln Mercury Inc.
- Orange Regional Medical Center
- Orbital
- Orbitz
- Orbus
- Orchard Hotel, San Francisco
- Oregon Alliance of Senior and Health Services
- Oregon Business District Association
- Oregon Convention Center
- Oregon Health and Science University Hospital
- Oregon Nisei Veterans
- Oregon State Pharmacists Association
- Orem Community Hospital
- Organ Donor Awareness Foundation
- Organ Recovery Systems
- Organic Media Inc.
- Organization Management Services
- Organized Community Action Program
- Orlando - Hilton Garden Inn Sea World, FL
- Orlando Chapter of Alpha Kappa Soroity
- Orlando Clinical Research Center
- Orlando Health
- Orlando Health Arnold Palmer Hospital
- Orlando Health H. Central Hospital
- Orlando Health Health Central