If Joakim Soria gets another save, and the 3 top closers (at least in total saves) continue to pitch well, this could be a record-tying year for closers. The three top closers (Rafael Soriano, Brian Wilson, Heath Bell) all have 40+ saves an ERA under 2.00. The only closer with 40+ saves and an ERA over 2.00 is Matt Capps, at 2.61.
They're all perilously closer to 2.00, though, with ERAs all between 1.82 and 1.87. If Rafael Soriano gave up only 1 run without recording an out, his ERA would jump up to 1.98. They've all come this far, so it's not a stretch to think they could all end up with an ERA under 2.00. Soria is at 39 saves, and has a 1.61 ERA, so he would be safe even with a bad outing (he could give up 2 runs without recording an out and still be barely above 1.90).
If all 4 of them finished with 40+ saves, and a sub-2.00 ERA, it would only be the 2nd time that has happened in ML history. A few bad innings could easily take it down from 3 or 4 closers to 0 or 1, but they've all pitched so well that seems unlikely.
40+ SV, 2.00 ERA or lower
4 2003 (Eric Gagne, Armando Benitez, John Smoltz, Billy Wagner)
3 2004 (Armando Benitez, Joe Nathan, Mariano Rivera)
3 1998 (Trevor Hoffman, Michael Jackson, Robb Nenn)
2 1990, 1993, 1997, 2002, 2005, 2008
1 1983, 1984, 1989, 1991, 1992, 1995, 1999, 2000, 2006, 2007, 2009)
0 1900-1982, 1985, 1986, 1987, 1988, 1994, 1996, 2001
Could there be 5 this year? Yes, it's possible. The only realistic (Mariano Rivera has the ERA, but he's only at 31 saves) chance is Billy Wagner, who has 35 saves, and a 1.43 ERA. With 12 games left, that's possible if the Braves play well and have some tight games.