I tried getting it off with my 3/8" socket; wouldn't come off.

Sprayed some "liquid wrench" on it and tried again with the 3/8".

Sprayed some more "liquid wrench" on it and tried a 1/2" to 3/8" adapter and a 1/2 wrench (very hard to get to fit in the engine compartment BTW).

All to no avail!

Sprayed a very liberal amount of Liquid Wrench on it and trying it in the morning with more light... Maybe I can use my torque wrench as a breaker bar.

Any help/advice?

The small engine comartment is really starting to piss me off. I'm dreadfully afraid of stripping the O2 sensor and never being able to get it out. SHIT