Oleic acid is a fatty acid found in animal and vegetable oils. It is called a mono-unsaturated fatty acid because of the single double bond between the carbons. It's physical properties are determined by the number, geometry, and position of this double bond and the degree of unsaturation.

Oleic acid is a mono-saturated fat generally believed to be good for one's health. Indeed, it is the chief fatty acid found in olive oil, comprising 55 to 85 percent of the important substance, which is commonly used in Mediterranean cuisine and has been hailed for its therapeutic characteristics since antiquity. Modern studies support the notion of the benefits of consuming olive oil, since evidence suggests that oleic acid helps lower levels of harmful low-density lipoproteins (LDLs) in the bloodstream, while leaving levels of beneficial high-density lipoproteins (HDLs) unchanged. Found also in significant quantities in canola, cod liver, coconut, soybean, and almond oils, oleic acid can be consumed from a variety of sources, some of which may soon contain even higher levels of the valuable fatty acid due to the efforts of genetic engineers.

OLEIC ACID, QsHaA, an organic acid occurring as a glyceride, triolein, in nearly all fats, and in many oils—olive, almond, cod liver. It appears as a by-product in the manufacture of candles. To prepare it, olive oil is saponified with potash, and lead acetate added; the lead salts are separated, dried, and extracted with ether, which dissolves the lead oleate; the solution is then treated with hydrochloric acid, the lead chloride filtered off, the liquid concentrated, and finally distilled under diminished pressure. Oleic acid is a colorless, odorless solid, melting at 14 and boiling at 223 (10 mm.). On exposure it turns yellow, becoming rancid. Nitric acid oxidizes it to all the fatty acids from acetic to capric. Nitrous acid gives the isomeric elaidic acid, which is crystalline and melts at 51. Hydriodic acid reduces both oleic and elaidic acids to stearic acid. Erucic acid, and the isomeric brassidic acid, belong to the oleic acid series. They occur as glycerides in rapeseed oil, in the fatty oil of mustard, and in the oil of grape seeds. Linoleic acid, found as glyceride in drying oils, and ricinoleic acid, found as glyceride in castor oil, closely resemble oleic acid.

Oleic acid occurs naturally in greater quantities than any other fatty acid. It is present as glycerides in most fats and oils. High concentrations of oleic acid can lower blood levels of cholesterol. It is used in the food industry to make synthetic butters and cheeses. It is also used to flavor baked goods, candy, ice cream, and sodas.