| Ostial Corporation | California |
| osTicket | Louisiana |
| Ostra Cybersecurity, Inc. | |
| Ostro | |
| Oswego State University of New York | New York |
| Osyte, Inc. | Washington |
| OTC Markets Group, Inc. | |
| OTech, Inc. | Texas |
| OTELCO | Maine |
| Otelier | Georgia |
| Other Ocean Group, Inc. | California |
| Otherlove | |
| OtherSide Entertainment, Inc. | |
| Oticara, Inc. | |
| Oticon | New Jersey |
| Otis AI | New York |
| Otixo, Inc. | California |
| OTO.Coach, Inc. | |
| Otolith Labs | District of Columbia |
| Otologic Technologies, Inc. | Wisconsin |
| Otomagnetics, Inc. | Maryland |
| OtoNexus Medical Technologies, Inc. | Washington |
| OTONOMI | New York |
| Otorio Ltd | |
| OTOY, Inc. | California |
| OTraces | Maryland |
| OTraces, Inc. | Maryland |
| Otricath | Texas |
| OTS Solutions, LLC | New Jersey |
| OTSI | Kansas |
| Otsuka America Pharmaceutical, Inc. | |
| Ott Consulting | New York |
| OTT, Inc. | Minnesota |
| Ottawa University | Kansas |
| Otter Creative Studio | |
| Otter PR | |
| Otter Products, LLC | Colorado |
| Otter Technologies, Inc. | |
| Otter.ai | California |
| Otterbein University | Ohio |
| OtterTune | Pennsylvania |
| Ottimate | |
| Otto | Texas |
| Ottomate | |
| Ottometric | |
| OTU Medical | California |
| Otuvy, Inc. | |
| Ouachita Baptist University | Arkansas |
| Our Designs Work, Inc. | |
| Our Hometown, Inc. | |