public utility, enterprise that provides certain classes of services to the public, including common carrier transportation (buses, airlines, railroads, motor freight carriers, pipelines, etc.); telephone and telegraph; power, heat, and light; and community facilities for water, sanitation, and similar services. In most countries such enterprises are state-owned and state-operated, but in the United States they are mainly privately owned and are operated under close governmental regulation.

The classic explanation for the need to regulate public utilities is that they are enterprises in which the technology of production, transmission, and distribution almost inevitably leads to complete or partial monopoly—that they are, in a phrase, natural monopolies. The monopolistic tendency arises from economies of scale in the particular industry, from the large capital costs typical of such enterprises, from the inelasticity of demand among consumers of the service, from considerations of the excess capacity necessary to meet demand peaks, and other considerations. It is often also the case that the existence of competing parallel systems—of local telephones or natural gas, for example—would be inordinately expensive, wasteful, and inconvenient. Given the tendency to monopoly and the potential therefore of monopolistic pricing practices, public regulation has for more than a century been applied to certain classes of business.

In practice, regulation aims to ensure that the utility serves all who apply for and are willing and able to pay for its services, that it operates in a safe and adequate manner, that it serves all customers on equal terms, and that its rates are just and reasonable. All states have regulatory commissions, and the federal government has several, including the Interstate Commerce Commission, the Civil Aeronautics Board, the Federal Power Commission, the Federal Communications Commission, and the Securities and Exchange Commission.

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