Penetrating oil is a type of lubricant designed to seep into tight spaces and loosen rusted or corroded parts. It is commonly used in mechanical applications to help free stuck bolts, nuts, and other fasteners. The oil's low viscosity allows it to penetrate small gaps, making it effective for maintenance and repair tasks. These oils typically contain a blend of petroleum-based oils and additives that enhance their ability to break down rust and corrosion. Popular brands of penetrating oil include WD-40, Liquid Wrench, and PB Blaster. Users often apply it by spraying or soaking the affected area for optimal results.