Power system reliability investigation is an important activity in both vertically incorporated and unbundled electric power utilities. New planning criteria with broader engineering consideration of transmission entrée and reliable risk assessment must be explicitly addressed. This research work introduces the concept of applying reliability index probability distributions to measure mass electric system risk. Bulk electric system reliability recital index probability distributions are used as integral elements in a performance based regulation method. The system well-being notion presented in this paper is a probabilistic framework that incorporates the accepted deterministic N − 1 security criterion, and provides precious information on what the degree of the system susceptibility might be under a particular system condition using a quantitative elucidation of the degree of system security and insecurity. An overall reliability investigation framework taking into accounts both adequacy and security perspectives are projected. The system planning process using combined adequacy and security considerations offers a supplementary reliability-based dimension.