Assuming you have the V-6 engine, it has two downstream (after the cats) O2 sensors and two upstream (before the cats) Air/Fuel Ratio Sensors. So the answer to your question is two O2 sensors.
The 2007 Nissan Xterra has 24 valves.
The 2007 Nissan Xterra has a V6 engine.
The 2007 Nissan Xterra is a gas-powered vehicle.
The 2007 Nissan Xterra has a 6-speed manual.
The 2007 Nissan Xterra has a 27.3 degrees angle of departure.
The maximum payload of the 2007 Nissan Xterra is 1138 lbs..
The 2007 Nissan Xterra has a 30.5 degrees angle of approach.
The curb weight of the 2007 Nissan Xterra is 4150 lbs..
The height of the 2007 Nissan Xterra is 6 ft. 2.9 in. (74.9 in.).
The 2007 Nissan Xterra's turning circle is 37.7 ft..
The 2007 Nissan Xterra runs on regular unleaded.
The 2007 Nissan Xterra is 14 ft. 10.7 in. (178.7 in.) long.