United States Senate elections, 2010 Senate composition at the beginning of the Senate composition at the beginning of the

| D_39_ | D_40_ | D_41_ | D_42_ | D_43_ | D_44_ | D_45_ | D_46_ | D_47_ | D_48_ |
|---|---|---|---|---|---|---|---|---|---|
| Majority→ | Majority→ | Majority→ | Majority→ | Majority→ | Majority→ | Majority→ | Majority→ | Majority→ | D 49 O |
| R 41 O | R 42 + | R 43 + | R 44 + | R 45 + | R 46 + | R 47 + | D 51 O | D 50 O | D 49 O |
| R 40 O | R 39 O | R 38 O | R 37 O | R 36 O | R 35 O | R 34 √ | R 33 √ | R 32 √ | R 31 √ |
| R 21 | R 22 | R 23 | R 24 √ | R 25 √ | R 26 √ | R 27 √ | R 28 √ | R 29 √ | R 30 √ |