2001 lexus is300 i dont know what o2 sensor to replace. My car smells like fuel and is getting horrible gas mileage..the check engine light is on and dont know which one to replace and dont have access to a scanner

 

You can get a code reader off ebay or amazon for under $10 (elm327 unit) and then free apps for your phone. Or go to any auto parts store and they will loan you one. Reading the codes is the place to start.

Bad mpgs and fuel smell is likely much more than a bad O2 sensor I would think.

 

I'm into keeping my vehicle stock, but after looking at your spoilers, I"m going with http://www.dallasautomotiverestyling.com/