Petroleum refining creates, as byproducts, many useful olefin (alkene) and aromatic checmicals, which are used in making many other products -- plastics, solvents, detergents, additives for lubricants, and more. There are a great many olefins and aromatics (ethylene, propylene, butadiene, benzene, toluene, and xylene being major ones). I didn't want to worry about handling each of these chemicals separately, so I've created a single generic product encompassing them all.