Functional unbundling is the separation of component parts of a previously unified product or service usually provided by a single party into distinct products or services each provided by different parties. In an unbundled market, consumers in the energy sector no longer have to buy transmission service, marketing and storage from the same supplier. A vertically integrated utility that has to undergo unbundling is often required to choose one component service in which it will specialize and restructure or divest itself of all parts of its business related to services in which it will not participate