If you're dealing with rusted bolts, the best penetrating oil to use isWD-40. WD-40 is a water displacement formula that quickly loosens rust and corrosion from metal surfaces. It's also great for freeing up stuck or frozen parts. Just spray it on, let it sit for a few minutes, and then start working the bolt back and forth until it comes loose. You can also use WD-40 to protect metal surfaces from rust and corrosion by spraying it on and wiping away any excess.