Best Penetrating Oil
Kind of surprising, but that mix (50-50) is what I
use.
Word of caution - don't use a foam cup to mix it in. (Yeah, don't ask me how I
know this) 
I mix mine in a glass jar with a good sealed lid - it does loose its
effectiveness after time - it's best to mix up a small "fresh" batch for best
results. I then pour it into an ALL metal squirt can to apply/use.
April 2007 "Machinist's Workshop" magazine comparison test wrote:
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 oil | Average load | Price per fluid ounce |
| None | 516 pounds | ------ |
| WD-40 | 238 pounds | $0.25 |
| PB Blaster | 214 pounds | $0.35 |
| Liquid Wrench | 127 pounds | $0.21 |
| Kano Kroil | 106 pounds | $0.75 |
| ATF-Acetone mix | 53 pounds | $0.10 (50/50 mix) |
The ATF-Acetone mix was a "home brew" mix of 50 - 50 automatic transmission
fluid and acetone.
Note the "home brew" was better than any commercial product in this one
particular test.
Note also that "Liquid Wrench" is about as good as "Kroil" for about 20% of the
price.