I copied this from OTT.com and believe me it works like a champ.
[Machinist's Workshop MagT recently published some information on various penetrating oils. The magazine reports they tested penetrates for break out torque on rusted nuts.They are below. They arranged a subjective test of all the popular penetrates with the control being the torque required to remove the nut from a "scientifically rusted" environment.
Penetrating oils ........... Average torque load to loosen
No Oil used ................... 516 pounds
WD-40 ..................... ... 238 pounds
PB Blaster .................... 214 pounds
Liquid Wrench ...............127 pounds
Kano Kroil .................... 106 pounds
ATF*-Acetone mix............53 pounds
The ATF-Acetone mix is a "home brew" mix of 50 - 50 automatic transmission fluid and acetone. Note this "home brew" released bolts better than any commercial product in this one particular test.
ATF-Acetone mix is best, but you can also use ATF and lacquer thinner in a 50-50 mix.
*ATF=Automatic Transmission Fluid.]