Essential liquids, such as oils, are substances that are necessary for the proper functioning of a system. Oils are a type of essential liquid that are composed of long-chain hydrocarbons and are used in many industries, including food production, cosmetics, and lubrication. They are also used to create fuel, such as diesel and gasoline. Oils are typically extracted from plants or animals, and can be found in a variety of forms, including vegetable, mineral, and synthetic.