When a system is in a state which differs from that of the infinite atmosphere surrounding it, its capacity to do work is measured by the maximum work which the system is capable of producing as it interacts with the infinite sink and eventually reaches the same state as the sink. When the system is subjected to a process there is, in general, a work interaction between the system and the surroundings, together with an exchange of heat with a source or with a sink other than the infinite sink. Here the actual change in available energy is compared with the ideal change in available energy. An efficiency for the process is defined, which will reflect all the losses or irreversibilities in the process. Hitherto, the definition of efficiency for any process from a purely thermodynamic viewpoint has been hampered by using different fundamental relationships in flow and nonflow processes, and for the flow process analysis it has been restricted to adiabatics in which the well-known parameter called `effectiveness' is used as a criterion of efficiency. In the analysis given here the same basic relationships are used independent of the circumstances in which the process takes place. This has been achieved by introducing the concept of `high-grade' energy.