The Bottom Line. In recent years, many U.S. energy firms have reorganized their slow-growing, yet stable businesses, such as pipelines and storage terminals, into master limited partnerships, or MLPs. There are some important differences between buying shares of a corporation and buying a stake in an MLP. With MLPs, investors buy units of the partnership, rather than shares of stock, and are referred to as unitholders. There are two classes of MLP owner: general partners and limited partners. General partners manage the day-to-day operations of the partnership. An MLP technically has no employees, so all services, from management to bookkeeping, are provided by the general partner.