Abstract The fundamental concepts associated with quantitative reliability assessment of electric power systems are reasonably well established and accepted by the power industry. The evaluation of the costs and benefits of competing investments has now become a standard practice in power system planning. In order to make a consistent appraisal of economics and reliability, it is imperative to compare the investment cost needed to attain a specified level of reliability with the reliability worth or benefits derived by the society at that level of system reliability. Customer interruption costs, which serve as surrogates for the perceived worth of supply reliability, have been determined for several jurisdictions, areas, provinces, and countries as diverse as Canada, United Kingdom, Nepal, and Thailand, among others. This paper extends the well-being framework to include the societal worth of electric service reliability in subtransmission systems associated with the above four countries/systems. Systems well-being is defined in terms of the three system states of healthy, marginal, and at risk, thus combining the deterministic and probabilistic approaches into a single framework. The main objective of the paper is to present results of reliability worth indices of expected cost of interruptions (ECOST) and interrupted energy assessment rate (IEAR), for both the healthy and at risk states in the well-being framework. The concepts associated with extending the well-being framework to include reliability worth parameters are illustrated by application to a small reliability test system designated RBTS. Customer interruption data from the four countries are used in conjunction with the RBTS subtransmission system in order to obtain the reliability worth indices.