Oil-based defoamers are high-efficiency antifoaming agents composed of carrier oils (mineral, vegetable, or synthetic oils) combined with hydrophobic particles and auxiliary additives. Their core mechanism relies on the carrier oil rapidly spreading over the foam film surface while hydrophobic particles act as active centers to rupture the foam membranes, working synergistically to accelerate liquid drainage and film collapse. These defoamers demonstrate excellent compatibility and persistence, being particularly suitable for various oil-based systems and some weakly alkaline aqueous systems, while maintaining stable performance even under harsh conditions like high temperature and pressure. They are widely applied in industrial fields including lubricants, metalworking fluids, petroleum extraction, oil-based coatings, and resin synthesis, effectively controlling surface foam and entrained air to improve production processes and product quality. While offering significant cost-effectiveness advantages, their use requires caution in systems demanding high transparency.