O
| Title | Date of creation | Surname | Current status | Notes |
|---|---|---|---|---|
| O'Brien of Ardtona | 1916 | O'Brien | extinct 1916 | first Baronet created Baron Shandon in 1918 |
| O'Brien of Kilfenora | 1891 | O'Brien | extinct 1914 | first Baronet created Baron O'Brien in 1900 |
| O'Brien of Merrion Square and Borris-in-Ossory | 1849 | O'Brien | dormant | Lord Mayor of Dublin; sixth Baronet died 1982 |
| O'Loghlen of Drumcanora | 1838 | O'Loghlen | extant | |
| O'Malley of Rosehill | 1804 | O'Malley | extinct 1892 | |
| O'Connell of Lakeview | 1869 | O'Connell | extant | |
| O'Neill of Cleggan | 1929 | O'Neill | extant | first Baronet created Baron Rathcavan in 1953 |
| Oakes of Hereford | 1815 | Oakes | extinct 1927 | first Baronet had already been created a Baronet in 1813, which creation became extinct in 1822 |
| Oakes of Nassau | 1939 | Oakes | extant | |
| Oakes of the Army | 1813 | Oakes | extinct 1822 | first Baronet obtained a new patent in 1815, which creation became extinct in 1927 |
| Oakshott | 1959 | Oakshott | extant | first Baronet created a life peer as Baron Oakshott in 1964, which title became extinct in 1975 |
| Ochterlony of Ochterlony | 1823 | Ochterlony | extinct 1964 | had already been created Baronet of Pitforthy in 1816, which title became extinct in 1825 |
| Ochterlony of Pitforthy | 1816 | Ochterlony | extinct 1825 | also created Baronet of Ochterlony in 1823, which title became extinct in 1964 |
| Ogle of Worthy | 1816 | Ogle | extinct 1940 | |
| Ohlson of Scarborough | 1920 | Ohlson | extant | |
| Oppenheimer of Stoke Poges | 1921 | Oppenheimer | extant | |
| Ormsby of Cloghans | 1812 | Ormsby | extinct 1833 | |
| Orr-Ewing of Ballikinran | 1886 | Orr-Ewing | extant | |
| Orr-Ewing of Hendon | 1963 | Orr-Ewing | extant | first Baronet created a life peer as Baron Orr-Ewing in 1971, which title became extinct in 1999 |
| Orr-Lewis of Whitewebbs Park | 1920 | Orr-Lewis | extinct 1980 | |
| Osler of Norham Gardens | 1911 | Osler | extinct 1919 | |
| Otway of Brighthelmstone | 1831 | Otway | extinct 1912 | |
| Ouseley of Claremont | 1808 | Ouseley | extinct 1889 | |
| Outram of The Bengal | 1858 | Outram | extant | |
| Owen of Orielton | 1813 | Owen | extinct 2002 |
Read more about this topic: List Of Baronetcies In The Baronetage Of The United Kingdom