| Occupational Advice Service | Academic & Science |
| Oklahoma Academy of Science | Academic & Science |
| Ohio Academy of Science | Academic & Science |
| Ophthalmic Anesthesia Society | Academic & Science |
| Online Assessment System | Academic & Science |
| Overpayments and Accounting Summary | Accounts and Finance |
| Occupational Wages structure | Business |
| Office Administrative Secretary | Business |
| Office of Audit Services | Business |
| Oshikai Advertising Services | Business |
| Optimum Additive Solution | Chemistry |
| On American Soil: How Justice Became a Casualty of World War II | Community |
| Olympic Archery in Schools | Community |
| Operation Animal Shelter | Community |
| Open Alternative School | Community |
| Organization of American States | Computer and Networking |
| Oracle Advanced Security | Computing |
| Open Application Server | Computing |
| Online Auction Site | Computing |
| On Access Scanner | Computing |
| Object Addressable Storage | Computing |
| Orbiter Avionics Software | Computing |
| Office Automation Systems | Computing |
| One Angry Swede | General |
| Office of Aviation Services's | General |
| Office of Aviation Services | General |
| Organisation armée secrète | General |
| Organization of Arab States | General |
| Objective Advantage Scope | General |
| Ordinary Attire Studio | General |
| Office of Addiction Services | General |
| Online Admission System | General |
| Occupational Assessment Services | General |
| Oakland Animal Services | General |
| Oil Activity Surface | General |
| Ola's Auto Services | General |
| Oman Auto Show | General |
| Isuzu Oasis | General |
| Option Adjust Spread | General |
| Office of Administrative Services | General |
| Online Assisted Support | General |
| Other American States | General |
| Option Adjusted Spreads | General |
| Oneonta Auxiliary Services | General |
| Obstacle Assessment Surface | General |
| Odisha Administrative Service | General |
| Office of Applied Studies | Governmental |
| Organisation de l’Armée Secrète | Governmental |
| Orissa Administative Service | Governmental |
| Offshore Access System | Governmental |
| Old Age Security | Governmental |
| Office of Aircraft Services | Governmental |
| Online Application System | Internet |
| Oral allergy syndrome | Medical |
| On Active Service | Military and Defence |
| Operations Automation System | Military and Defence |
| Offensive Air Support | Military and Defence |
| Oracle Application Server | Networking |
| Organization of African States | Regional |
| Organization of Agreement States | Regional |
| Organisation of American States | Regional |
| Office Administration System | Softwares |
| Office Automation System | Space Science |
| Orbiter Aeroflight Simulator | Space Science |
| Orbiter Atmospheric Simulator | Space Science |
| Orbiter Avionics System | Space Science |
| Oregon Adaptive Sports | Sports |
| Option Adjusted Spread | Stock Exchange |
