| Onyx II | 30.21 | 2005 | Nautor Swan |
| Onyx 2 | 38.2 | 1990 | Elsflether Werft GmbH & Co. KG |
| Onyx | 33.53 | 2019 | Riva S.p.A. |
| Only One I | 28.27 | 2008 | Overmarine Group SPA |
| Only Now | 34.6 | 2012 | Tansu Yachts |
| Only Now | 31.72 | 2003 | CNB - Construction Navale Bordeaux |
| Only Ice | 31.04 | 2016 | Azimut Yachts |
| Onika | 39.62 | 2014 | Delta Marine |
| Oneworld | 31.68 | 2018 | Gulf Craft |
| One by One | 28.65 | 2003 | Custom Line |
| One Zero | 37.11 | 2024 | Numarine |
| One Shot | 28.17 | 2012 | Ocean Alexander |
| One O One | 36 | 2008 | Tecnomar |
| One O One | 30.78 | 2007 | Tarrab Yachts |
| One My Way | 27.6 | 2014 | Sanlorenzo |
| One More Time | 28.01 | 1992 | Lydia Yachts |
| One More Time | 28.35 | 2020 | Horizon Yachts |
| One More | 30 | 1989 | Baglietto S.p.A. |
| One Force | 40 | 2013 | Costruzioni Navali Tigullio - Castagnola |
| One Blue | 38.71 | 2009 | BPT Trade |
| One & Only | 32 | 2020 | Azimut Yachts |
| One | 27.6 | 2006 | Pershing S.p.a. |
| One | 34.13 | 2025 | Van der Valk Shipyard |
| One | 75.75 | 2025 | Feadship |
| On Time | 34.16 | 2024 | Sanlorenzo |
| On Seafari | 32.89 | 1985 | Broward Marine |
| On Q | 27.95 | 2017 | Hatteras Yachts |
| Omnia 1 | 48.7 | 2015 | Bilgin Yachts |
| Omnia | 61 | 1974 | Amels |
| Omnia | 46 | 2017 | Brodosplit Inc. |
| Omega Lyuks | 37 | 1982 | Wisla Stocznia |
| Omaha | 49.9 | 2018 | Heesen Yachts |
| Oma | 32 | 2019 | Azimut Yachts |
| Olympus | 28.4 | 1929 | New York Yacht & Launch Co |
| Olympus | 55 | 1996 | Feadship |
| Olympia | 57 | 2002 | Feadship |
| Olokun | 49.99 | 2020 | Tankoa Yachts S.p.A. |
| Olmida | 48.77 | 2010 | Royal Hakvoort Shipyard |
| Olivia RB | 29.22 | 2019 | Pearl Yachts |
| Olivia O | 88.51 | 2020 | Ulstein Verft AS |
| Olivia | 37.54 | 2023 | Gulf Craft |
| Oli | 35.5 | 2016 | Benetti SpA |
| Olga | 34.44 | 1986 | Cantieri di Pisa |
| Olde Salt | 34 | 2015 | Aegean Yacht |
| Olan | 31.68 | 2023 | Gulf Craft |
| Ol'iva B | 30.69 | 2002 | Falcon Yachts S.r.l. |
| Okto | 66.4 | 2014 | ISA Yachts |
| Okto | 31.04 | 2012 | Azimut Yachts |
| Oktana | 38.5 | 1995 | Codecasa S.p.A. |
| Oktamar | 40 | 2014 | Liman JSC Shipbuilding Yard |
