2000 Ford Ranger Oxygen Sensor

They best way is to climb under the truck and take a look. They look like spark plugs threaded into your exhaust system.

I would say there is probably 3 o2 sensors on your ranger. One in each exhaust manifold and one after the 2nd catalytic converter.

The sensors themselves arent expensive, they are just a pain in the butt to remove from the bung on the exhaust. Usually they are rust welded to the exhaust and have to be heated with a torch to remove