Oleo, commonly known as oleomargarine or simply margarine, is a type of fat used as a substitute for butter. It is made from vegetable oils, animal fats, or a combination of both, and is often blended with water, milk, or other ingredients to create a spreadable consistency. Oleo is popular for cooking and baking due to its versatility and lower cost compared to butter. The production of oleo began in the 19th century as a response to the demand for affordable fat sources. Today, it is available in various forms, including sticks, tubs, and spreads, and is often fortified with vitamins such as vitamin D and vitamin A to enhance its nutritional value.