The first motor oils were plain mineral oil, which lubricated, cooled, and sealed the engines of the first automobiles. But modern engines and driving habits make greater demands on a motor oil. Today's motor oils are composed of lubricating oils called base stocks (about 80 to 90 percent) and additives (about 10 to 20 percent). Base stocks are either "conventional"-made from crude oil-or "synthetic"-made from chemicals. Additives are chemicals that are dissolved in the base stock to improve its properties, characteristics, or performance. Through the careful combination of these ingredients in exactly the right amounts, lubricants can be tailored for specific applications.