The current party composition of the Senate is:
| Senator | State | Party | First elected | Seat Up |
|---|---|---|---|---|
| Daniel Akaka | Hawaii | Democrat | 1990 | 2006 |
| Lamar Alexander | Tennessee | Republican | 2002 | 2008 |
| Wayne Allard | Colorado | Republican | 1996 | 2008 |
| George Allen, Jr | Virginia | Republican | 2000 | 2006 |
| Max Baucus | Montana | Democrat | 1978 | 2008 |
| Evan Bayh | Indiana | Democrat | 1998 | 2004 |
| Robert Bennett | Utah | Republican | 1992 | 2004 |
| Joseph Biden, Jr | Delaware | Democrat | 1972 | 2006 |
| Jeff Bingaman | New Mexico | Democrat | 1982 | 2006 |
| Christopher S. Bond | Missouri | Republican | 1986 | 2004 |
| Barbara Boxer | California | Democrat | 1992 | 2004 |
| John Breaux | Louisiana | Democrat | 1986 | 2004 |
| Sam Brownback | Kansas | Republican | 1996 | 2004 |
| Jim Bunning | Kentucky | Republican | 1998 | 2004 |
| Conrad Burns | Montana | Republican | 1988 | 2006 |
| Robert Byrd | West Virginia | Democrat | 1958 | 2006 |
| Ben Nighthorse Campbell | Colorado | Republican | 1992 | 2004 |
| Maria Cantwell | Washington | Democrat | 2000 | 2006 |
| Thomas Carper | Delaware | Democrat | 2000 | 2006 |
| Lincoln Chafee | Rhode Island | Republican | 2000 | 2006 |
| Saxby Chambliss | Georgia | Republican | 2002 | 2008 |
| Hillary Rodham Clinton | New York | Democrat | 2000 | 2006 |
| Thad Cochran | Mississippi | Republican | 1978 | 2008 |
| Norm Coleman | Minnesota | Republican | 2002 | 2008 |
| Susan Collins | Maine | Republican | 1996 | 2008 |
| John Cornyn | Texas | Republican | 2002 | 2008 |
| Kent Conrad | North Dakota | Democrat | 1986 | 2006 |
| Jon Corzine | New Jersey | Democrat | 2000 | 2006 |
| Larry Craig | Idaho | Republican | 1990 | 2008 |
| Mike Crapo | Idaho | Republican | 1998 | 2004 |
| Thomas Daschle | South Dakota | Democrat | 1986 | 2006 |
| Mark Dayton | Minnesota | Democrat | 2000 | 2006 |
| Mike DeWine | Ohio | Republican | 1994 | 2006 |
| Christopher Dodd | Connecticut | Democrat | 1980 | 2004 |
| Elizabeth Dole | North Carolina | Republican | 2002 | 2008 |
| Pete Dominici | New Mexico | Republican | 1972 | 2002 |
| Byron Dorgan | North Dakota | Democrat | 1992 | 2004 |
| Richard Durbin | Illinois | Democrat | 1996 | 2008 |
| John Edwards | North Carolina | Democrat | 1998 | 2004 |
| John Ensign | Nevada | Republican | 2000 | 2006 |
| Mike Enzi | Wyoming | Republican | 1996 | 2008 |
| Russ Feingold | Wisconsin | Democrat | 1992 | 2004 |
| Dianne Feinstein | California | Democrat | 1992 | 2006 |
| Peter Fitzgerald | Illinois | Republican | 1998 | 2004 |
| William Frist | Tennessee | Republican | 1994 | 2006 |
| Bob Graham | Florida | Democrat | 1986 | 2004 |
| Lindsey Graham | South Carolina | Republican | 2002 | 2008 |
| Chuck Grassley | Iowa | Republican | 1980 | 2004 |
| Judd Gregg | New Hampshire | Republican | 1992 | 2004 |
| Charles Hagel | Nebraska | Republican | 1996 | 2008 |
| Tom Harkin | Iowa | Democrat | 1984 | 2008 |
| Orrin Hatch | Utah | Republican | 1976 | 2006 |
| Ernest Hollings | South Carolina | Democrat | 1966 | 2004 |
| Kay Bailey Hutchison | Texas | Republican | 1993 | 2006 |
| James Inhofe | Oklahoma | Republican | 1994 | 2006 |
| Daniel Inouye | Hawaii | Democrat | 1962 | 2004 |
| James Jeffords | Vermont | Independent | 1988 | 2006 |
| Tim Johnson | South Dakota | Democrat | 1996 | 2008 |
| Edward Kennedy | Massachusetts | Democrat | 1962 | 2006 |
| John Kerry | Massachusetts | Democrat | 1984 | 2008 |
| Herb Kohl | Wisconsin | Democrat | 1988 | 2006 |
| Jon Kyl | Arizona | Republican | 1994 | 2006 |
| Mary Landrieu | Louisiana | Democrat | 1996 | 2008 |
| Frank Lautenberg | New Jersey | Democrat | 1982 | 2006 |
| Patrick Leahy | Vermont | Democrat | 1974 | 2004 |
| Carl Levin | Michigan | Democrat | 1978 | 2008 |
| Joseph Lieberman | Connecticut | Democrat | 1988 | 2006 |
| Blanche Lincoln | Arkansas | Democrat | 1998 | 2004 |
| Trent Lott | Mississippi | Republican | 1988 | 2006 |
| Richard Lugar | Indiana | Republican | 1976 | 2006 |
| John McCain | Arizona | Republican | 1986 | 2004 |
| Mitch McConnell | Kentucky | Republican | 1984 | 2008 |
| Barbara Mikulski | Maryland | Democrat | 1986 | 2004 |
| Zell Miller | Georgia | Democrat | 2000 | 2004 |
| Lisa Murkowski | Alaska | Republican | 2003 | 2004 |
| Patty Murray | Washington | Democrat | 1992 | 2004 |
| Ben Nelson | Nebraska | Democrat | 2000 | 2006 |
| Bill Nelson | Florida | Democrat | 2000 | 2006 |
| Don Nickles | Oklahoma | Republican | 1980 | 2004 |
| Mark Pryor | Arkansas | Democrat | 2002 | 2008 |
| Jack Reed | Rhode Island | Democrat | 1996 | 2008 |
| Harry Reid | Nevada | Democrat | 1986 | 2004 |
| Pat Roberts | Kansas | Republican | 1996 | 2008 |
| Jay Rockefeller | West Virginia | Democrat | 1984 | 2008 |
| Rick Santorum | Pennsylvania | Republican | 1994 | 2006 |
| Paul Sarbanes | Maryland | Democrat | 1976 | 2006 |
| Charles Schumer | New York | Democrat | 1998 | 2004 |
| Jeff Sessions | Alabama | Republican | 1996 | 2008 |
| Richard Shelby | Alabama | Republican | 1986 | 2004 |
| Gordon Smith | Oregon | Republican | 1996 | 2008 |
| Olympia Snowe | Maine | Republican | 1994 | 2006 |
| Arlen Specter | Pennsylvania | Republican | 1980 | 2004 |
| Debbie Stabenow | Michigan | Democrat | 1998 | 2006 |
| Ted Stevens | Alaska | Republican | 1968 | 2008 |
| John E. Sununu | New Hampshire | Republican | 2002 | 2008 |
| Jim Talent | Missouri | Republican | 2002 | 2006 |
| Craig Thomas | Wyoming | Republican | 1994 | 2006 |
| George Voinovich | Ohio | Republican | 1998 | 2004 |
| John Warner | Virginia | Republican | 1978 | 2008 |
| Ron Wyden | Oregon | Democrat | 1996 | 2004 |