Kentucky Republican Jim Bunning‘s retirement announcement on Monday was the eighth by a senator whose seat is on a 2010 ballot. Barring a major surprise, that’s probably the last Senate retirement that will be announced this election cycle.

The eight “open” Senate seats is above the average for the past few election cycles, more than the five in 2008 or the four in 2006 and matching the eight in 1994 and 2004. In the past three decades, only in the 1996 cycle were there more open Senate seats (13) than in 1994, 2004 or 2010.

Though the retirement announcement by Bunning, who was hampered by poor fundraising and approval ratings, probably increases the Republican Party’s chances of holding his seat, open seats often are more difficult for the defending party to retain than those that incumbents are defending.