I need to remove the O2 sensor from the exhaust. What is the easiest way most have found to do this? I sprayed some penetrating oil on it hoping to free it. But putting a wrench on it doesn't seem to make it budge. Do I need to heat up the area around the sensor to remove it? Will running the truck and letting the exhaust heat up do the trick?

 

Yea heat the bung with a torch but ovoid heating the sensor, system should be cold otherwise.

If it still fails to come loose heat the bung around it getting it fairly hot, then touch a couple ice cubes to the sensors wrench boss, have a few cubes in a bowl right there handy.
Hit it with the ice right after taking the heat away, the ice will suddenly contract the sensor slightly and that sudden shock will really aid in freeing it.