Currently, Republicans control the Senate 51-48-1. However, when it comes to retaking the Senate, the numbers are actually slightly different. This is because:

• Zell Miller is really a Republican
• Jim Jeffords is really a Democrat
• John Kerry will become President, and Romney will appoint a Republican

All together, this means that from the standpoint of Senate control after November 2nd, Republicans currently hold the Senate 53-47. Here is a map based on this standpoint (blue for double Democrat, red for double Republican, and purple for a split state):

In order for Democrats to be in control (even if it is the bizarre position of controlling the Senate despite being technically down 50-49-1 but controlling the Vice-Presidency and being allied with the Independent), Democrats need a net gain of three seats. In November, there are 34 Senate seats up for election. With Zell Miller as a Republican, 18 of those seats belong to Democrats, and 16 to Republicans. For Democrats to take the Senate in the highly unusual minority controlled fashion described above, they need to win 21 of these elections. To win the Senate outright, they need to win 22 of those elections (which would reproduce the 50-49-1 Democratic edge of 2001 and 2002).

Of the 18 Democratic seats, 13 are considered safe (although Washington, California, North Dakota, Wisconsin and Nevada are not hard-core locks). Of the 16 Republican seats, 9 are probably safe (although Kentucky, Ohio and New Hampshire are not in the bag). These leaves control at 46-42 Republican plus tight races, or 43-37 Republican plus all conceivable races. In the tight-race scenario, Democrats must win 9 of the 12 races to take outright control (8 for the minority control scenario). In the all conceivable races scenario, Democrats must win 14 out of 20 to take the Senate outright (13 would be enough for minority control).

The 20 states that could conceivably be close races are Alaska, California, Colorado, Florida, Georgia, Illinois, Kentucky, Louisiana, Missouri, Nevada, New Hampshire, North Carolina, North Dakota, Pennsylvania, Ohio, Oklahoma, South Carolina, South Dakota, Washington and Wisconsin. In 2000, Bush won eight of these states by double digits. Gore won two of these states by double digits, and less than ten points decided ten.

On their excellent Senate page, Kos, Jerome and Stephan Yellin provide detailed information on all of these races. For somewhat less-informed people (such as myself), I hope this quick breakdown of the numbers needed in order for Democrats to retake control is a useful add-on.