| Abbreviation | Definition |
|---|---|
| OC | Oregon City |
| ODOS | Occupied Density Of States |
| OECS | Organisation Of Eastern Caribbean States |
| OK | klahoma |
| OK | Ohio and Kentucky |
| OK | Oklahoma |
| OK | Old Kentucky |
| OMGUS | of the Military Government United States |
| OMGUS | of the Military Governor United States |
| OMS | Organization of MISO States |
| ONC | Office of the National Coordinator |
| ONSC | Ozark Natural Science Center |
| OP | Overland Park, Kansas |
| OR | Oregon |
| OSES | Oil States Energy Services |
| OSPV | Oil States Piper Valve |
| OT | Oklahoma and Texas |
| OTUS | Of The United States |
| OVR | Ohio Valley Region |
| OWRB | Oklahoma Water Resource Board |