List of former members of the United States House of Representatives (O) Number of years/terms representative/delegate has served Number of years/terms representative/delegate has served

| Representative | Years | State_ | Party | Lifespan |
|---|---|---|---|---|
| Lewis P. Ohliger | 1892–1893 | Ohio | Democratic | 1843–1923 |
| J. Van Vechten Olcott | 1905–1911 | New York | Republican | 1856–1940 |
| Pearl Peden Oldfield | 1929–1931 | Arkansas | Democratic | 1876–1962 |
| William Allan Oldfield | 1909–1928 | Arkansas | Democratic | 1874–1928 |
| Edson B. Olds | 1849–1855 | Ohio | Democratic | 1802–1869 |
| Abram B. Olin | 1857–1863 | New York | Republican | 1808–1879 |
| Gideon Olin | 1803–1807 | Vermont | Democratic-Republican | 1743–1823 |
| Henry Olin | 1824–1825 | Vermont | National Republican | 1768–1837 |
| Jim Olin | 1983–1993 | Virginia | Democratic | 1920–2006 |
| Andrew Oliver | 1853–1857 | New York | Democratic | 1815–1889 |
| Daniel C. Oliver | 1917–1919 | New York | Democratic | 1865–1924 |
| Frank A. Oliver | 1923–1934 | New York | Democratic | 1883–1968 |
| James C. Oliver | 1937–1943 | Maine | Republican | 1895–1986 |
| James C. Oliver | 1959–1961 | Maine | Democratic | 1895–1986 |
| Mordecai Oliver | 1853–1855 | Missouri | Whig | 1819–1898 |