The Spermaceti organ found in the heads of sperm whales produces an oily/waxy substance. There can be up to 2 tonnes of oil in each animal. It's also produced in smaller quantities in some other whale species.

Before whaling was made illegal (in most countries) there was a large market for the oil, which was used in lamps, candles, medicines and for specialist lubrication.

There are three main theories regarding its possible function(s).

• As an adjustable buoyancy device
• As a buffer in collisions
• As a bio-sonar echo resonator

To date, no theory has been agreed upon.

See: Wikipedia