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 |
|---|---|---|---|---|
| William C. Oates | 1881–1894 | Alabama | Democratic | 1835–1910 |
| James Oberstar | 1975–2011 | Minnesota | Democratic | 1934– |
| Dave Obey | 1969–2011 | Wisconsin | Democratic | 1934– |
| Thomas P. Ochiltree | 1883–1885 | Texas | Independent | 1837–1902 |
| Benjamin Barker Odell, Jr. | 1895–1899 | New York | Republican | 1854–1926 |
| Moses F. Odell | 1861–1865 | New York | Democratic | 1818–1866 |
| N. Holmes Odell | 1875–1877 | New York | Democratic | 1828–1904 |
| Charles F. Ogden | 1919–1923 | Kentucky | Republican | 1873–1933 |
| David A. Ogden | 1817–1819 | New York | Federalist | 1770–1829 |
| Henry W. Ogden | 1894–1899 | Louisiana | Democratic | 1842–1905 |
| Alexander Ogle | 1817–1819 | Pennsylvania | Democratic-Republican | 1766–1832 |
| Andrew Jackson Ogle | 1849–1851 | Pennsylvania | Whig | 1822–1852 |
| Charles Ogle | 1837–1841 | Pennsylvania | Anti-Masonic | 1798–1841 |
| Charles Ogle | 1841 | Pennsylvania | Whig | 1798–1841 |
| Woodson R. Oglesby | 1913–1917 | New York | Democratic | 1867–1955 |