| Code | Name | Region |
|---|---|---|
| USOAB | Offshore Ambrose | |
| USOSP | Ocean Springs | MS |
| USOCX | Ocean View | DE |
| USOIW | Ocean View | NJ |
| USNTU | Oceana | VA |
| USOCI | Oceanic | AK |
| USVQC | Oceano | CA |
| USOCP | Oceanport | NJ |
| USOCN | Oceanside | CA |
| USXJX | Oceanside | NY |
| USOC5 | Oceanview | NJ |
| USONW | Oceanway | FL |
| USC7H | Ochelata | OK |
| USOCG | Ochlocknee | GA |
| USOC8 | Ochopee | FL |
| USOLA | Ocilla | GA |
| USOCM | Ocoee | FL |
| USOC7 | Ocoee | TN |
| USOZE | Ocoee, Polk | TN |
| USOCO | Oconomowoc | WI |
| USOCQ | Oconto | WI |
| USOAW | Oakwood, Buchanan | VA |
| USOWU | Oakwood, Oakland | MI |
| USOKG | Oakwood, Paulding | OH |
| USOXX | Oasis | CA |
| USOMX | Oatman | AZ |
| USXOR | Oberlin | OH |
| USOBE | Obetz | OH |
| USOBI | Obion | TN |
| USO6G | Oblong | IL |
| USOIN | O'brien | FL |
| USOCF | Ocala | FL |
| USO9C | Occidental | CA |
| USOCY | Ocean | NJ |
| USOB3 | Ocean Beach | CA |
| USOCE | Ocean City | MD |
| USOEC | Ocean City | NJ |
| USOAM | Ocean Gate | NJ |
| USOBH | Ocean Isle Beach | NC |
| USOCA | Ocean Reef | FL |
| USOS8 | Ocean Shores | WA |
| USIM5 | Oaklandon | IN |
| USOQY | Oakley | CA |
| USKLY | Oakley | IL |
| USOQK | Oakley | KS |
| USOK4 | Oakley | MI |
| USOK8 | Oakley | UT |
| USOXM | Oakman | AL |
| USUXS | Oakmont | PA |
| USOQR | Oakridge | OR |