| Operational Transistor Amplifier | Academic & Science |
| Online Trading Academy | Academic & Science |
| OchraToxin A | Academic & Science |
| Mota | Airport Code |
| Orascom Telecom Algeria | Business |
| Orthodontic Technicians Association | Business |
| Online Travel Agent | Business |
| Online Travel Agency | Business |
| Online Travel Agents | Business |
| One Time Adjustment | Business |
| Online travel agencies | Business |
| Office of Tax Appeals | Business |
| Open Travel Alliance | Business |
| Organic Trade Association | Business |
| Ontario Trucking Association | Business |
| Ortho-tolidine-arsenite | Chemistry |
| Ohio Township Association | Community |
| Ohio Trucking Association | Community |
| Oregon Trucking Association | Community |
| Oregon Truck Associations | Community |
| Oregon Trucking Associations | Community |
| Oregon Telecommunications Association | Community |
| Office of Internal Administration | Community |
| One To All | Community |
| Orthopaedic Trauma Association | Community |
| Over-the-Air Activation | Computer and Networking |
| Oracle Training Administration | Computing |
| Optical Transmit Asymmetry | Computing |
| One Touch Activation | Computing |
| Opitcal Tube Assembly | Computing |
| Overall Track | Computing |
| Office of the Telecommunications Adjudicator | Computing |
| Operational Transconductance Amplifier | Electronics |
| Oxford Text Archive | General |
| Office of the Tenant Advocate | General |
| Office of Technical Assistance | General |
| Optional Taco Accessories | General |
| Optical Trapping Applications | General |
| Organized Team Activity | General |
| Obedience Trials Association | General |
| Orchard Training Area | General |
| Oil Transmission Automatic | General |
| Offroad Turn Assist | General |
| Offroad Trucks Australia | General |
| Ontario Time Attack | General |
| Organizatia Turismului Si Automobilului | General |
| Oregon Truck Association | General |
| Oshawa Truck Assembly | General |
| Oklahoma Trucking Association | General |
| Oil To Air | General |
| Ontario Temperance Act | Governmental |
| Oklahoma Turnpike Authority | Governmental |
| Online Trust Alliance | Governmental |
| Office of Therapeutics Alliances | Governmental |
| Other Transaction Authority | Governmental |
| Office of Tax Analysis | Governmental |
| On-Time Arrival | Governmental |
| Officers Training Academy | Indian Ministry of Home Affairs |
| Occupational Therapy Assistant | Jobs |
| Occupational Therapy Assistants | Medical |
| Office of Technology Assessment | Military and Defence |
| One True Army | Military and Defence |
| Officer Traning Academy (of India) | Military and Defence |
| Off the Air | News & Entertainment |
| Optical Tube Assembly | Physics Related |
| Ottoman Turkish | Regional |
| Turkish, Ottoman (1500 - 1928) | Regional |
| Mota, Ethiopia | Regional |
| Open Tools Api (application Programming Interface) | Softwares |
| Optical Telescope Assembly | Space Science |
| Ontario Tennis Association | Sports |
| Organized Team Activities | Sports |
| Off-season Team Activities | Sports |
| Ontario Tennis Association's | Sports |
| Office of Technology Alliances | Technology |
| Origin Technology Age | Technology |
| Over The Air | Telecommunication |
