| Abbreviation | Definition |
|---|---|
| OJB | Ohio Power Company Class B |
| OK | Old Kent Financial Corporation |
| OKE | OneOk, Inc. |
| OLN | Olin Corporation |
| OLS | Olsten Corporation |
| OMC | Omnicom Group, Inc. |
| OMC | Omnicom Group, Incorporated |
| OMG | O M Group, Inc. |
| OMG | O M Group, Incorporated |
| OMI | Owens & Minor, Incorporated |
| OMM | OMI Corporation |
| OMN | OMNOVA Solutions, Inc. |
| OMS | Oppenheimer Multi Sector Fund |
| OMX | OfficeMax, Inc. |
| ONB | Old National Bancorp |
| ONE | Bank One Corporation |
| ONEPB | Bank One Corporation Preferred B |
| ONEPC | Bank One Corporation Preferred C |
| ONEPT | Bank One Capital I |
| OO | Oakley, Incorporated |