| Oamaru & Dunedin Steam Co Ltd |
| Oamaru Harbour Board |
| Onehunga Sawmilling Co |
| Oparara Shipping Co Ltd |
| Opihi Shipping Co Ltd |
| Opouri Shipping Co Ltd |
| Opua Shipping Co Ltd |
| Orepuki Shipping Co Ltd |
| Otago Harbour Board |
| Otago Harbour Cruises Ltd |
| Otago Iron rolling Mills |
| Otago Steam Ship Co Ltd |
| Otago Towing Co Ltd |
| Otago Trawling & Distribution |
| Otea Mining Co Ltd |