This paper discusses several probabilistic analytical methods and tools such as contingency enumeration, multi-area reliability assessment, and Monte Carlo simulation that can be used for transmission planning, generation expansion and system reliability assessment. The paper includes some case study results of applying these probabilistic methods and tools to real system planning and analysis. One study quantifies network probabilistic reliability measures with respect to various system problems, including branch overloads, loss of loads, voltage limit violations, and voltage collapse conditions as identified in contingency analysis for an EHV electric grid. The probabilistic measures complement the deterministic contingency results.