| Abbreviation | Definition |
|---|---|
| OSTX | Ostex International, Inc. |
| OSULP | O'Sullivan Industries Holdings |
| OSYS | Osteo Systems, Inc. |
| OSYSE | Osteo Systems, Inc. |
| OTCBB | Over-The-Counter Bulletin Board |
| OTCM | Royce Microcap Trust, Inc. |
| OTCX | O T C America |
| OTES | OP-Tech Environmental Services |
| OTEX | Open Text Corporation |
| OTFC | Oregon Trail Financial Corporation |
| OTGS | O T G Software, Inc. |
| OTIX | Orthodontixs, Inc. |
| OTLC | O T Computer Training Corporation |
| OTMN | O T Mining Corporation |
| OTRI | Outright Industries, Inc. |
| OTRKB | Oshkosh Truck Corporation Class B |
| OTRKB | Oshkosh Truck Corporation Class B (de-listed) |
| OTRKB | Oshkosh Truck Corporation Class B (de-listed) |
| OTSH | O T S Holdings, Inc. |
| OTTR | Otter Tail Power Company |