The races are ranked by most likely to switch parties and I have separate rankings for seats currently held by Democrats and seats currently held by Republicans. The approval numbers are from SurveyUSA's most recent 50-state tracking poll and are as of August 17. The polling numbers are the most recent from Rasmussen in addition to the most recent non-Rasmussen poll I could find (no partisan funded polls included and no online Zogby). Also included is the composite numbers from the last 5 polls taken in the race according to Pollster.com. Cash on hand numbers are the Second Quarter numbers filed with the FEC and are current as of June 30 unless otherwise noted.
| Rank | State | Seat | Approval Rating | Candidates | Rasmussen Poll | Other Poll | Pollster.com | Money Race (COH) |
| 1 | Pennsylvania | Rick Santorum | 48 - 45 | Republican Rick Santorum Democrat Bob Casey | Casey 48 Santorum 40 (8/22) | Casey 56 Santorum 38 (8/27) | Casey 51 Santorum 40 | Santorum $9.4 million Casey $5.2 million |
| 2 | Ohio | Mike DeWine | 42 - 48 | Republican Mike DeWine Democrat Sherrod Brown | Brown 47 DeWine 41 (9/14) | Brown 46 DeWine 40 (8/27) | Brown 46 DeWine 40 | DeWine $6.6 million Brown $3.7 million |
| 3 | Montana | Conrad Burns | 39 - 55 | Republican Conrad Burns Democrat Jon Tester | Tester 52 Burns 43 (9/13) | Tester 48 Burns 45 (8/27) | Tester 47 Burns 44 | Burns $2.2 million Tester $0.5 million |
| 4 | Rhode Island | Lincoln Chafee | 51 - 44 | Republican Lincoln Chafee Democrat Sheldon Whitehouse | Whitehouse 44 Chafee 42 (8/23) | Chafee 43 Whitehouse 42 (8/21) | Whitehouse 43 Chafee 40 | Whitehouse $1.5 million Chafee $0.8 million (Through 8/23) |
| 5 | Missouri | Jim Talent | 52 - 41 | Republican Jim Talent Democrat Claire McCaskill | McCaskill 45 Talent 42 (9/12) | McCaskill 48 Talent 47 (9/13) | Talent 48 McCaskill 45 | Talent $6.9 million McCaskill $2.7 million (Through 7/19) |
| 6 | Tennessee | Bill Frist | Retiring | Republican Bob Corker Democrat Harold Ford | Corker 45 Ford 44 (9/5) | Ford 48 Corker 45 (9/11) | Ford 45 Corker 45 | Ford $1.8 million Corker $1.2 million (Through 7/14) |
| 7 | Virginia | George Allen | 51 - 38 | Republican George Allen Democrat James Webb | Allen 50 Webb 43 (9/12) | Allen 48 Webb 45 (9/12) | Webb 46 Allen 46 | Allen $6.6 million Webb $0.4 million |
| 8 | Arizona | Jon Kyl | 53 - 36 | Republican Jon Kyl Democrat Jim Pederson | Kyl 52 Pederson 35 (8/24) | Kyl 46 Pederson 36 (8/29) | Kyl 49 Pederson 40 | Kyl $6.7 million Pederson $1.5 million (Through 8/23) |
| 9 | Nevada | John Ensign | 50 - 38 | Republican John Ensign Democrat Jack Carter | Ensign 46 Carter 39 (7/31) | Ensign 54 Carter 33 (8/12) | Ensign 50 Carter 38 | Ensign $3.2 million Carter $0.4 million (Through 7/26) |
| 10 | Texas | Kay Bailey Hutchison | 61 - 32 | Republican Kay Bailey Hutchison Democrat Barbara Ann Radnofsky | Hutchison 58 Radnofsky 32 (8/31) | None | Hutchison 55 Radnofsky 35 | Hutchison $9.2 million Radnofsky $0.3 million |
| 11 | Utah | Orrin Hatch | 60 - 34 | Republican Orrin Hatch Democrat Pete Ashdown | No Poll Available | Hatch 61 Ashdown 27 (8/28) | Hatch 63 Ashdown 21 | Hatch $2.5 million Ashdown $13,000 |
| 12 | Maine | Olympia Snowe | 72 - 24 | Republican Olympia Snowe Democrat Jean Hay Bright | Snowe 68 Bright 20 (8/17) | Snowe 68 Bright 10 (7/21) | Snowe 64 Bright 24 | Snowe $2.2 million Bright $100 |
| 13 | Wyoming | Craig Thomas | 61 - 31 | Republican Craig Thomas Democrat Dale Groutage | Thomas 59 Groutage 32 (7/6) | None | Thomas 62 Groutage 29 | Thomas $1.0 million Groutage $4,000 (Through 8/2) |
| 14 | Mississippi | Trent Lott | 66 - 31 | Republican Trent Lott Democrat Erik Fleming | Lott 66 Fleming 29 (2/13) | None | N/A | Lott $2.0 million Fleming $600 |
| 15 | Indiana | Dick Lugar | 59 - 33 | Republican Dick Lugar | No Opposition | No Opposition | N/A | Lugar $4.0 million |
| Rank | State | Seat | Approval Rating | Candidates | Rasmussen Poll | Other Poll | Pollster.com | Money Race (COH) |
| 1 | New Jersey | Bob Menendez | 42 - 43 | Democrat Bob Menendez Republican Tom Kean | Kean 44 Menendez 39 (8/30) | Kean 43 Menendez 39 (8/27) | Kean 42 Menendez 40 | Menendez $7.4 million Kean $2.3 million |
| 2 | Maryland | Paul Sarbanes | Retiring | Democrat Ben Cardin Republican Michael Steele | Cardin 47 Steele 42 (8/9) | Cardin 44 Steele 39 (8/25) | Cardin 47 Steele 40 | Steele $3.1 million Cardin $1.6 million (Through 8/23) |
| 3 | Minnesota | Mark Dayton | Retiring | Democrat Amy Klobuchar Republican Mark Kennedy | Klobuchar 47 Kennedy 40 (8/28) | Klobuchar 50 Kennedy 40 (8/27) | Klobuchar 49 Kennedy 41 | Kennedy $3.4 million Klobuchar $3.0 million (Through 8/23) |
| 4 | Michigan | Debbie Stabenow | 51 - 42 | Democrat Debbie Stabenow Republican Michael Bouchard | Stabenow 51 Bouchard 43 (8/31) | Stabenow 54 Bouchard 34 (9/12) | Stabenow 50 Bouchard 41 | Stabenow $4.4 million Bouchard $0.5 million (Through 7/19) |
| 5 | Washington | Maria Cantwell | 55 - 38 | Democrat Maria Cantwell Republican Mike McGavick | Cantwell 52 McGavick 35 (9/6) | Cantwell 56 McGavick 39 (8/27) | Cantwell 52 McGavick 39 | Cantwell $6.4 million McGavick $1.1 million |
| 6 | Connecticut | Joe Lieberman | 53 - 43 | Democrat Ned Lamont Republican Alan Schlesinger Independent Joe Lieberman | Lieberman 45 Lamont 43 Schlesinger 6 (9/14) | Lieberman 51 Lamont 38 Schlesinger 7 (9/11) | Lieberman 48 Lamont 39 Schlesinger 4 | Lieberman $3.5 million Lamont $0.4 million Schlesinger $76,000 (Through 7/19) |
| 7 | Nebraska | Ben Nelson | 67 - 27 | Democrat Ben Nelson Republican Pete Ricketts | Nelson 55 Ricketts 32 (8/10) | None | Nelson 54 Ricketts 33 | Nelson $2.1 million Ricketts $1.1 million |
| 8 | West Virginia | Robert Byrd | 65 - 32 | Democrat Robert Byrd Republican John Raese | Byrd 63 Raese 30 (9/5) | Byrd 59 Raese 30 (5/22) | Byrd 59 Raese 31 | Byrd $2.6 million Raese $0.2 million |
| 9 | Vermont | Jim Jeffords | Retiring | Independent Bernie Sanders Republican Richard Tarrant | Sanders 62 Tarrant 34 (8/3) | Sanders 56 Tarrant 35 (7/27) | Sanders 63 Tarrant 29 | Sanders $1.7 million Tarrant $0.5 million (Through 8/23) |
| 10 | Florida | Bill Nelson | 47 - 38 | Democrat Bill Nelson Republican Katherine Harris | Nelson 57 Harris 34 (8/28) | Nelson 53 Harris 38 (9/13) | Nelson 57 Harris 29 | Nelson $12.1 million Harris $2.2 million (Through 8/16) |
| 11 | North Dakota | Kent Conrad | 74 - 21 | Democrat Kent Conrad Republican Dwight Grotberg | Conrad 57 Grotberg 35 (1/25) | None | N/A | Conrad $3.5 million Grotberg $19,000 |
| 12 | California | Dianne Feinstein | 53 - 42 | Democrat Dianne Feinstein Republican Dick Mountjoy | Feinstein 58 Mountjoy 35 (9/7) | Feinstein 56 Mountjoy 34 (8/27) | Feinstein 54 Mountjoy 32 | Feinstein $8.0 million Mountjoy $21,000 |
| 13 | Wisconsin | Herb Kohl | 56 - 37 | Democrat Herb Kohl Republican Robert Lorge | Kohl 59 Lorge 31 (8/10) | Kohl 63 Lorge 14 (7/2) | Kohl 57 Lorge 30 | Kohl $1.6 million Lorge $2,000 (Through 8/23) |
| 14 | New Mexico | Jeff Bingaman | 57 - 33 | Democrat Jeff Bingaman Republican Allen McCulloch | Bingaman 56 McCulloch 32 (9/12) | None | Bingaman 58 McCulloch 30 | Bingaman $1.8 million McCulloch $2,000 |
| 15 | New York | Hillary Clinton | 61 - 35 | Democrat Hillary Clinton Republican John Spencer | Clinton 61 Spencer 31 (7/31) | Clinton 62 Spencer 32 (9/7) | Clinton 58 Spencer 33 | Clinton $22.2 million Spencer $0.8 million (Through 8/23) |
| 16 | Delaware | Tom Carper | 59 - 30 | Democrat Tom Carper Republican Jan Ting | No Polling Available | None | N/A | Carper $2.5 million Ting $53,000 (Through 8/23) |
| 17 | Hawaii | Daniel Akaka | 51 - 40 | Democrat Daniel Akaka or Ed Case Republican Jerry Coffee or Mark Beatty | Akaka 58 Coffee 30 (7/31) | None | Akaka 58 Coffee 30 | Akaka $1.0 million Coffee (No Report) |
| 18 | Massachusetts | Ted Kennedy | 56 - 40 | Democrat Ted Kennedy Republican Kevin Scott or Kenneth Chase | No Polling Available | None | N/A | Kennedy $8.7 million Chase $34,000 |