This paper presents the results of a project performed for the Israel Electric Corporation, Ltd. (IEC), with the objective of developing the most cost-effective and technically feasible 300-MW CAES-plant concept with underground storage in an aquiferous reservoir. Three conceptually different turbomachinery trains are analyzed, including one based on the use of state-of-the-art combustion turbine components with high firing temperatures. The results are reported for each turbomachinery train concept, optimized for the geological conditions of two alternative underground-storage sites. Along with other generic findings, the paper concludes with the selection of a turbomachinery train, its cycle parameters and configuration, and underground storage site to be used for further preliminary engineering and cost estimates. The results are generalized for use in future CAES projects.