How many O2 sensors are there in a Ford 2002 F150 4.6?

The below answer can not be correct, because I just changed out my passenger side cat and the cat it self has an 02 sensor on it. So I do not know if there are three or four but I do know there is one on my cat.

We are getting ready to change ours and I'm almost positive that there are two front ones (on each manifold) and one after the cat. The front two are heated, make sure you get the correct ones, the back one is not heated. So to answer, there is 3 total o2 sensors.