pale yellow oil obtained with spermaceti from the head cavity (spermaceti organ) and blubber of the sperm whale. Formerly used as a superior lighting oil and later as a lubricant, it was little used in the modern period apart from in certain toiletries and pharmaceuticals, although in 1950 advances in oil chemistry allowed it to be used in large quantities for the manufacture of soap (soap and detergent).

After removal of spermaceti and treatment with sulfur, sperm oil provided excellent lubricants that resisted extreme pressures. These were commonly used in mechanical transmissions, high-speed machinery, and precision instruments. The oil was also hardened to make textile sizings (sizing). Saponification yielded fatty acids (fatty acid) for soap manufacture and fatty alcohols (alcohol) for cosmetics (cosmetic) and detergents (detergent).