OCC
- Francisco de Orellana Airport
- Kamen Rider OOO
- OC Châteaudun
- OFC Men's Champions League
- Oakland Community College
- Oakton Community College
- Occasionally connected computing
- Ocean County College
- Ocean Cruising Club
- Oceania Cycling Confederation
- Office of Child Care
- Office of the Comptroller of the Currency
- Officer Candidates Course
- Official Charts Company
- Ohio Capital Conference
- Ohio Cardinal Conference
- Ohno continuous casting
- Oklahoma Corporation Commission
- Online Compliance Consortium
- Onnuri Community Church
- Onondaga Community College
- Ontario Crafts Council
- Open Cloud Consortium
- Operation Christmas Child
- Operations Control Center
- Opportunity cost of capital
- Optical Cable Corporation
- Optimistic concurrency control
- Optimists Cricket Club
- Options Clearing Corporation
- Orange Coast College
- Orange County Choppers
- Orange County, California
- Oregon Convention Center
- Organic composition of capital
- Osborne Computer Corporation
- Ottawa Curling Club
- Ozark Christian College
- POWER8
- Portland, Oregon
- Science Communication Observatory
- The Oxford Companion to Chess
- Toronto