As of 2005, there are 55 Republicans, 44 Democrats, and 1 Independent (who was elected as a Republican) in the US Senate.

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D I

There are zero members of any third party.

No other country has fewer third-party seats than the USA.