O
| Town name | Postal code |
| Odendaalsrus | 9476 |
| Odendaalsrus | 9480 |
| Odendaalsrus | 9483 |
| Odin Park | 1830 |
| Odin Park | 1831 |
| Ogies | 2232 |
| Ogies | 2233 |
| Okiep | 8271 |
| Olifantsfontein | 1666 |
| Olifantsfontein | 1667 |
| Olifantshoek | 8450 |
| Onrus River | 7201 |
| Oos-Londen | 5201 |
| Oos-Londen | 5205 |
| Oos-Londen | 5207 |
| Oos-Londen | 5209 |
| Oos-Londen | 5241 |
| Oos-Londen | 5247 |
| Oos-Londen | 5275 |
| Oos-Londen | 5292 |
| Orange Farm | 1805 |
| Orange Farm | 1841 |
| Orange Grove | 2192 |
| Oranjeville | 1995 |
| Orkney | 2619 |
| Orkney | 2620 |
| Orkney | 2621 |
| Orkney | 2622 |
| Orkney | 2624 |
| Orkney | 2625 |
| Orkney | 2626 |
| Orkney | 2627 |
| Orlando | 1863 |
| Orlando | 1865 |
| Orlando | 1870 |
| Orlando | 1806 |
| Orlando | 1807 |
| Orlando | 1808 |
| Orlando | 1804 |
| Osizweni | 2952 |
| Ottery | 7750 |
| Ottery | 7780 |
| Ottery | 7800 |
| Ottery | 7941 |
| Ottosdal | 2610 |
| Oudshoorn | 6625 |
| Oudtshoorn | 6625 |
| Oudtshoorn | 6628 |
| Oudtshoorn | 6631 |
| Oudtshoorn | 6632 |
| Oudtshoorn | 6633 |
| Oudtshoorn | 6634 |
| Oudtshoorn | 6650 |
| Oudtshoorn | 6651 |
| Oudtshoorn | 6623 |
| Oudtshoorn | 6624 |
| Ozwatini | 3242 |
| Ozwatini | 3261 |
