Oleum
Oleum is a chemical. It does not have a chemical formula because it is a mixture, not a chemical compound. It is made by dissolving sulfur trioxide in sulfuric acid. It is part of the contact process used to make sulfuric acid. It is a fuming (releases toxic fumes) liquid. It can be dissolved in some water to produce concentrated sulfuric acid.
Oleum Media
Oleum fuming in air
