All Scotch whisky must be aged in oak barrels for at least three years. Any age statement on a bottle of Scotch whisky, expressed in numerical form, must reflect the age of the youngest whisky used to produce that product. A whisky with an age statement is known as guaranteed-age whisky. A whisky without an age statement is known as a no age statement (NAS) whisky, the only guarantee being that all whisky contained in that bottle is at least three years old. The minimum bottling strength according to the regulation is 40% alcohol by volume.