- Oakwood Southshore Medical Center
- Oakwood Village
- Oatfield Estates
- OBGyn of Lancaster, Inc.
- OCA Westchester and Hudson Valley Chapter
- OCASA International
- Occasions Caterers
- Ocean Center
- Ocean Energy Inc.
- Ocean Springs Hospital
- Ocean Walk Village
- Oceaneering International Inc.
- Oceaneering Space and Thermal Systems
- OCG
- OCH Regional Medical Center
- Ochsner Baptist Medical Center
- Ochsner Clinic Foundation
- Ochsner Health System
- Ochsner LSU Health Monroe
- Ochsner LSU Health Shreveport-Academic Medical Center
- Ochsner Medical Center
- Ochsner Medical Center - Baton Rouge
- Ochsner Medical Center - Kenner
- Ochsner Medical Center - North Shore
- Ochsner Medical Center - West Bank Campus
- Ochsner Medical Center Hancock
- Ochsner St. Anne Hospital
- Oconee County Board of Commissioners
- Oconee County Regional Airport
- Oconee Medical Campus
- Oconee Regional Cancer Center
- Oconomowoc Memorial Hospital
- Octogon Sports Marketing)
- Office Depot
- Office Masters Inc.
- Office of County Judge Dolores Briones
- Office of Health Commissioner
- Office of Homeland Security, The White House
- Office of Intergovernmental Affairs
- Office of Personnel Management for New Mexico
- Office of Samoan Affairs
- Office of the Assistant Secretary for Planning and Evaluation ASPE)
- Office of the Bronx Borough
- Office of the Clerk of Superior Court
- Office Solutions
- Official Meeting Facilities Guide
- Oficina Medicina Interna Dra. A. Melendez
- Oficina Procuradora del Paciente
- Oficirade La Procuradora de Las Mujeres
- Ogan Dallal Associates PR