Reliability of electrical service is a function of sufficient supply and consistent transmission capability. Reliability is compromised if there is too little energy created, or if too little capacity exists to carry it to the customer.

In most contexts where this term is used, adequate transmission capacity is a given. The system is expected to be capable of meeting the needs of the market. The overriding reliability concern in transmission is the ability of the system to deal with outages, equipment failures and other types of service interruption. The ability to manage these interruptions is referred to as a system's security.

Some industry-watchers are concerned that there may be an accountability gap in energy reliability in newly-deregulated markets. Energy producers are expected to make sufficient power available for the market, and transmission authorities are expected to make sufficient capacity available for delivery of the energy. But if either of these parties fails to meet its responsibilities, both sectors suffer.

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