Any of various viscous liquids used to lubricate the mechanical components of an internal combustion engine, with the primary purposes of reducing friction and wear on moving parts, cleaning and preventing the accumulation of sludge and varnish, improving the static seal created by gaskets and piston rings, and cooling the engine by carrying heat away from the moving parts. Modern commercial motor oils typically consist of a mixture of base oils produced from crude petroleum and enhanced with various additives, including detergents, dispersants, and other chemical protectants, which is then circulated under pressure through oil galleries in the engine block.