| OLISENS 2230911 · TMA1250251 | an individual | 5 Pharmaceuticals | Registered | 2024 |
| OLSEN 1926488 · TMA1134534 · design | ECR International Inc. | 11 Lighting | Registered | 2022 |
| OLSEN 1733072 · TMA1055782 | Olsen Holding GmbH | 18 Leather25 Clothing | Registered | 2019 |
| OLSEN 0619812 · TMA577908 | ECR International Inc. | 11 Lighting | Registered | 2003 |
| OLSON 2310030 · design | TAYLOR MADE GOLF COMPANY, INC. | 25 Clothing28 Toys | Pending | 2024 |
| OLSON 2310029 · design | TAYLOR MADE GOLF COMPANY, INC. | 28 Toys | Pending | 2024 |
| OLISNET 1819852 · TMA1016984 | CACEIS Bank | 36 Finance | Registered | 2019 |
| OLASCAN 2252151 | Olaplex, Inc. | 9 Electronics42 Science | Pending | 2023 |
| OWLGANGS 2261509 · TMA1281233 | an individual | 21 Housewares | Registered | 2025 |
| OLGSNTAE 2172376 · TMA1222351 | Chaozhou Xiduoduo Technology Co.Ltd. | 28 Toys | Registered | 2024 |
| OLIGONAVIGATOR 2157532 · TMA1231194 | an individual | 9 Electronics | Registered | 2024 |
| OLISMART 2053147 · TMA1168140 | Olipop Inc. | 32 Beer | Registered | 2023 |
| Oligonol 1886209 · TMA1077787 | AMINO UP CO. LTD. | 1 Chemicals5 Pharmaceuticals29 Meat+2 | Registered | 2020 |
| OLGONE 1538122 · TMA883358 | Exxon Mobil Corporation | 40 Treatment42 Science45 Legal | Registered | 2014 |
| OLIGOMATE 1515756 · TMA871047 | Kabushiki Kaisha Yakult Honsha (also trading as Yakult Honsha Co. Ltd.) | 30 Coffee | Registered | 2014 |
| OLIGOMEDICINES 1513053 · TMA840625 · design | Nitto Denko Avecia Inc. | 40 Treatment42 Science | Registered | 2013 |
| OligoMedicines 1502997 · TMA843655 | Nitto Denko Avecia Inc. | 40 Treatment42 Science | Registered | 2013 |
| OILSMART 1495408 · TMA830930 | The Clorox Company of Canada Ltd. | 5 Pharmaceuticals | Registered | 2012 |
| OLOGEN 1468966 · TMA820105 · design | BODY ORGAN BIOMEDICAL CORP. | 5 Pharmaceuticals10 Medical | Registered | 2012 |
| OLIGONOL 1282940 · TMA692058 | AMINO UP CO. LTD. | 1 Chemicals5 Pharmaceuticals | Registered | 2007 |
| OLIGONOL 1184334 · TMA670988 | AMINO UP CO. LTD. | 5 Pharmaceuticals | Registered | 2006 |
| OLLYSCAN 1123915 · TMA587448 | OS Debt Holders Investment Fund, LLC | 37 Construction42 Science | Registered | 2003 |
| OLIGOMER 1108818 · TMA629318 | Owner not shown | 3 Cosmetics | Registered | 2005 |
| OLHAUSEN 0869620 · TMA526169 | OLHAUSEN BILLIARD MANUFACTURING, INC. A CALIFORNIA CORPORATION | 28 Toys | Registered | 2000 |
| OLSONITE 0401036 · TMA233342 | Bemis Manufacturing Company (a Wisconsin corporation) | 11 Lighting | Registered | 1979 |