A research program aimed at the development of a molten salt thermal energy storage system commenced in June 1976. This topical report describes work performed under Task I: Salt Selection. A total of 31 inorganic salts and salt mixtures, including 9 alkali and alkaline earth carbonate mixtures, were evaluated for their suitability as heat-of-fusion thermal energy storage materials at temperatures of 850 °F to 1000°F. Thermo physical properties, safety hazards, corrosion, and cost of these salts were compared on a common basis. We concluded that because alkali carbonate mixtures show high thermal conductivity, low volumetric expansion onmelting, low corrosivity and good stability, they are attractive as heat-of-fusion storage materials in this temperature range. A 35 weight percent Li 2 C0 3-65 weight percent K 2 C0 3 (50 mole percent Li 2 CC>3-50 mole percent K 2 COj) mixture was selected as a model system for further experimental work. This is a eutectoid mixture having a heat of fusion of 148 Btu/lb (82 cal/g) that forms an equimolar compound, LiKCC^. The Li 2 C0 3-K 2 C03 mixture is intended to serve as a model system to define heat transfer characteristics,potential problems, and to provide "first-cut" engineering data required for the prototype system. The cost of a thermal energy storage system containing this mixture cannot be predicted until system characteristics are better defined. However, our comparison of different salts indicated that alkali and alkaline earth chlorides may be more attractive from a salt cost point of view. The long-.terrn corrosion characteristics and the effects of volume change on melting for the chlorides should be investigated to determine their overall suitability as a heat-of-fusion storage medium.