Vi har så langt registrert 19 632 rederier
| Navn | Grunnlagt | | Opstad, Ole, Midsund | |
| Opstad Shipping A/S, Midsund, Molde | |
| Optiroc A/S, Oslo | |
| Optiship A/S, Rubbestadneset | |
| O. P. Tvedt, Kragerø | |
| O. P. Tvedt. Porsgrunn | |
| O. P. Ugland, Arendal | |
| O. Puntervold, Egersund | |
| O. P. Werge, Brevik | |
| O. P. Wessel, Drammen | |
| O. P. Wingaard, Bergen | |
| Orbis Steamship Corp., New York | |
| Ore Carriers International Ltd., Monrovia | |
| O. Reinertsen, Farsund | |
| O. Reinertsen & Sønner, Farsund | |
| O. Reinhardt, Kristiansand | |
| Ore Steamship C. New York, NY. USA | |
| Ore Steam Ship Co Inc., New York | |
| O. R. Føreid, Grimstad | 1888 |
| Oriental Trade & Transport Co. Ltd. | |
| Orient Management Norway A/S, Bergen | |
| Orient Ship Management Norway A/S, Arendal / Oslo | |
| Orient Ship Management , Oslo | |
| Orient Steam Navigation Co.Ltd. , Glasgow. UK | |
| Origo Shipping A/S, Søreidgrend, Bergen | |
