cool things with wheels, since 2006
This method will work where penetrating oil will fail. If you got a rusted bolt in a blind hole, and you can't afford to have it break off, this is definitely the way to go.Side note: The best penetrating oil I have ever come across is a 50/50 mixture of acetone and ATF. Has one drawback though. It is extremely flammable, so you cannot use it in conjunction with heating with a torch.
I've heard of that mixture, and posted about it back in 2010 http://justacarguy.blogspot.com/2010/10/penetrating-oils-compared.html