| OKUR | OnKure Therapeutics, Inc. | Healthcare | $119M | — | 0 |
| ONT | Onterris, Inc. | Industrials | $608M | — | 0 |
| ONTO | Onto Innovation Inc. | Technology | $13.9B | — | 0 |
| ONWRF | Onward Medical N.V./ADR | — | — | — | 0 |
| OOMA | Ooma, Inc. | Communication Services | $602M | — | 0 |
| OPBK | OP Bancorp | Financial Services | $225M | — | 0 |
| OPAL | OPAL Fuels Inc. | Industrials | $52.0M | — | 0 |
| OPPPF | Open House Group Co. Ltd/ADR | — | — | — | 0 |
| OTEX | Open Text Corporation | Technology | $5.5B | — | 0 |
| OPENZ | Opendoor Technologies Inc. | — | — | — | 0 |
| OPLN | OPENLANE, Inc. | Consumer Cyclical | $3.7B | — | 0 |
| OPRA | Opera Limited | Communication Services | $1.6B | — | 0 |
| OPK | OPKO Health, Inc. | Healthcare | $1.2B | — | 0 |
| OPRT | Oportun Financial Corporation | Financial Services | $381M | — | 0 |
| OPY | Oppenheimer Holdings Inc. | Financial Services | $1.3B | — | 0 |
| OPFI | OppFi Inc. | Financial Services | $533M | — | 0 |
| OPXS | Optex Systems Holdings, Inc | Industrials | $72.7M | — | 0 |
| CYVNY | Opthea Ltd | — | — | — | 0 |
| OCC | Optical Cable Corporation | Technology | $126M | — | 0 |
| OPTH | Optimi Health Corp. | Healthcare | $15.8M | — | 0 |
| OPRX | OptimizeRx Corp. | Healthcare | $148M | — | 0 |
| OPTU | Optimum Communications, Inc. | Communication Services | $488M | — | 0 |
| OPHC | OptimumBank Holdings, Inc. | Financial Services | $113M | — | 0 |
| OPCH | Option Care Health, Inc. | Healthcare | $3.4B | — | 0 |
| IRD | Opus Genetics, Inc. | Healthcare | $402M | — | 0 |