| OpenVision, Inc. | South Carolina |
| OpenVPN | California |
| OpenVZ | Washington |
| OpenWater | California |
| Openwave Computing, LLC | New York |
| OpenWith.org | California |
| OpenX | California |
| OpenXcell | Nevada |
| Opera Bioscience | |
| Operand | |
| Operant AI, Inc. | California |
| Operatic Agency, Inc. | |
| Operation Code | Oregon |
| Operation Nation, LLC | |
| Operation Technology | |
| Operation Web SEO Company | California |
| Operational Systems, Inc. | Colorado |
| Operations Assistance | Connecticut |
| Operative | New York |
| Operator Collective | California |
| Operator Headgap Systems, Inc. | Tennessee |
| Operator Interface Technology, Inc. | Colorado |
| Operator, Inc. | |
| OPEX Communications, Inc. | California |
| Opex Technologies | North Carolina |
| Opexa Therapeutics, Inc. | |
| Opexus | |
| OpGen, Inc. | Maryland |
| Ophanic | |
| Ophelia | |
| Ophidion, Inc. | |
| OPHIR RF | California |
| Ophirex, Inc. | California |
| Opin Systems | Minnesota |
| Opiniator | |
| Opiniion | Utah |
| OPKIX, Inc. | California |
| Opko Health, Inc. | Florida |
| Ople.ai | California |
| OPM Mastery, Inc. | Nevada |
| Opolis Marketing | |
| OporaSolutions, LLC | |
| Oppenheimer & Co., Inc. | |
| Opportunities 2 Serve, LLC | |
| Opportunity Finance Network | District of Columbia |
| Opportunity Hub, Inc. | |
| Opprtna Therapeutics | |
| Opprtunity, Inc. | California |
| Opptly | Texas |
| OPS Consulting, LLC | |