| OSBK | Oconee Financial Corporation | Financial Services | $50.9M | — | 0 |
| OCTLF | Octave Intelligence plc | — | — | — | 0 |
| OSG | Octave Specialty Group, Inc. | Financial Services | $186M | — | 0 |
| OCGN | Ocugen, Inc. | Healthcare | $343M | — | 0 |
| OCUL | Ocular Therapeutix, Inc. | Healthcare | $2.2B | — | 0 |
| OCSAW | Oculis Holding AG | — | — | — | 0 |
| OVTZ | Oculus VisionTech, Inc. | Technology | $2.8M | — | 0 |
| ODERF | Odakyu Electric Railway Co., Ltd. | Industrials | $3.9B | — | 0 |
| ODD | Oddity Tech Ltd. | Consumer Defensive | $1.0B | — | 0 |
| ODYS | Odysight.ai Inc. | Technology | $52.0M | — | 0 |
| ODYY | Odyssey Health, Inc. | Healthcare | $1.0M | — | 0 |
| OMEX | Odyssey Marine Exploration, Inc. | Basic Materials | $41.1M | — | 0 |
| ODTX | Odyssey Therapeutics, Inc. | Healthcare | $957M | — | 0 |
| OFAL | OFA Group | Industrials | $0.6M | — | 0 |
| OPAD | Offerpad Solutions Inc. | Real Estate | $16.2M | — | 0 |
| OPI | Office Properties Income Trust | Real Estate | $1.2B | — | 0 |
| OFG | OFG Bancorp | Financial Services | $2.2B | — | 0 |
| OFSSO | OFS Capital Corporation - | Financial Services | $45.0M | — | 0 |
| OCCIM | OFS Credit Company, Inc. | Financial Services | $684M | — | 0 |
| OGE | OGE Energy Corp. | Utilities | $9.1B | — | 0 |
| OVBC | Ohio Valley Banc Corp. | Financial Services | $208M | — | 0 |
| OMH | Ohmyhome Limited | Real Estate | $1.1M | — | 0 |
| OIS | Oil States International, Inc. | Energy | $500M | — | 0 |
| ODC | Oil-Dri Corporation of America | Basic Materials | $1.3B | — | 0 |
| OIOWW | OIO Group | Financial Services | $0.6M | — | 0 |