| OSTRUM 1874862 · TMA1088580 | an individual | 36 Finance | Registered | 2020 |
| OSTRIM 0840559 · TMA525262 | PROTOS, INC. | 5 Pharmaceuticals29 Meat30 Coffee | Registered | 2000 |
| OSTRAL 2291548 | Devimco Immobilier Inc. | 36 Finance37 Construction42 Science | Pending | 2023 |
| OSTRO 2165766 · TMA1235782 | Nokia Corporation | 9 Electronics | Registered | 2024 |
| OSETRA 1780020 · TMA981178 | DAVID YURMAN IP LLC | 14 Jewellery35 Advertising | Registered | 2017 |
| OSTARA 1764622 · TMA1027001 | Ostara Biomedical Limited | 5 Pharmaceuticals10 Medical | Registered | 2019 |
| OSTARA 1664524 · TMA934138 | Ostara Nutrient Recovery Technologies Inc. | 1 Chemicals40 Treatment | Registered | 2016 |
| OSTRO 1636170 · TMA961989 | Topaz International Enterprises Limited | 14 Jewellery | Registered | 2017 |
| OSTARA 1565085 · TMA855514 | Ostara Nutrient Recovery Technologies Inc. | 1 Chemicals40 Treatment | Registered | 2013 |
| OSTAR 1249482 · TMA655224 | OSRAM GmbH | 9 Electronics | Registered | 2005 |
| ÖSTARA 2282920 | an individual | 35 Advertising44 Medical | Pending | 2023 |
| OSTRYA 2238197 · design | 9385-9395 Quebec Inc. | 6 Metal8 Hand9 Electronics+6 | Pending | 2023 |
| Ostrich 2058261 · TMA1170913 | an individual | 9 Electronics | Registered | 2023 |
| OCTARAY 1869261 · TMA1041189 | Biosense Webster, Inc. | 10 Medical | Registered | 2019 |
| Ossetra 1379714 · TMA794852 | IC Spa Products Inc. | 3 Cosmetics41 Education | Registered | 2011 |
| OXSTRIN 1274014 · TMA748241 | NUTRAMAX LABORATORIES, INC. (A Maryland Corporation) | 5 Pharmaceuticals | Registered | 2009 |
| OAKTRAK 1016124 · TMA562295 | MIRZA INTERNATIONAL LIMITED | 18 Leather25 Clothing | Registered | 2002 |
| OCTORAL 1005488 · TMA537212 | an individual | 2 Paints | Registered | 2000 |
| OSITREE 2282786 · design | Guangzhou Huatu Cosmetic Technology Co. Ltd. | 3 Cosmetics | Pending | 2023 |
| OCXTREM 2153400 · design | an individual | 25 Clothing | Pending | 2021 |
| OCTORDLE 2254744 · TMA1274489 | MERRIAM-WEBSTER, INCORPORATED | 41 Education | Registered | 2024 |
| OSTER 2222345 · TMA1243251 | Sunbeam Products, Inc. | 7 Machines8 Hand11 Lighting+1 | Registered | 2024 |
| OASTRO 2197348 · TMA1237379 | Shenzhen Shengning Dianzishangwu Co., Ltd | 21 Housewares | Registered | 2024 |
| OakTrust 2171145 · TMA1221514 | OakTrust Investment Management Limited | 35 Advertising36 Finance41 Education | Registered | 2024 |
| OOHSTORE 2150950 · TMA1217337 | Oohpod Limited | 35 Advertising | Registered | 2024 |