Originally posted by COntour:
Correction, I replaced my O2 sensor last weekend and there are what appear to be 3. 
There are the ones mentioned above, and then there is another one, I don't have my car with me since it's in the shop, but if you look under the car you can see all three. One you can see by looking under the hood, and the other two you have to put the car up on ramps. 
You should have 4, your car is a '97 which uses OBDII, it has two before cat O2, and two aftercat O2. '95 has only two sensors, and both are before cat.
