oxigen sensor

I have a Nissan Altima GXE 2.4 l engine, 4 cil.
it sucks on gas mileage. I get around 19 mpg. Somebody told me to change the O2 sensor and the mpg will going to improve. Anyone knows something about this thing?
tks

It will improve only if the O2 is bad or weak. But do a search for oxygen sensor or 02.

How Stuff Works is a great site to visit http://auto.howstuffworks.com/question257.htm

Your check engine light should be on. It will help you diagnose the part that is causing the problem in your car. When your engine starts, it uses a pre set fuel mixture until it warms up a bit. When an O2 sensor fails the computer doesn't actually guess anything. The computer quits useing the information from the sensors (O2 is one of the sensors) and uses the same pre set fuel mixture used during the first few seconds after starting. O2 sensors become contaminated by the exhaust and more sluggish to send accurate signals. You should be getting 50% better fuel mileage. Very likely your problem is more serios than a bad O2 sensor. 2.4L Altimas have two O2 sensors. The greatest risk is that so much unburned fuel is going through your catalitic converter that the converter will get so hot that the insides will melt and clog the exhaust and can even cause a fire on the ground or in the car. Clogged exhaust is another possibility that will cause the loss of fuel mileage you report.

i dunno about that, ive replaced lots of 02 sensors, and no mil has been on. watching datastreams, and seeing open loop after 10 minutes, wen all other sensors are good is a good indicator that ur 02 is gone, or if it isnt cycling.

i think ur problem is an 02