Firm capacity is the amount of energy available for production or transmission which can be (and in many cases must be) guaranteed to be available at a given time. Firm energy refers to the actual energy guaranteed to be available. For instance in the transmission of natural gas a pipeline company would provide its customers with the right to use ‘firm capacity’ within the transportation (and storage) system. Other than in exceptional circumstances (such as during periods of planned maintenance) this firm capacity is expected to be available at all times and enables Shippers to transport gas, subject to conditions, into and/or out of the system