How Many 02 Sensors?

I have a 2005 sedan with the 3.4. It's coming up on 100,000 miles and I'm going to change the oxygen sensor(s). Does anyone know if there are 1 or 2?

2 I beleive, one in ft of the cat and one after, the one behind the cat should not need to be replaced.

Thanks Maxwedge. Is there something different about the one behind the catalytic converter so that it shouldn't need to be changed?

It just monitors the cat, has no performance effect.

Hey, thanks for the great info maxwedge.