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A summary of the research carried out prior to the start and during the first half of this project is presented. A description of the geothermal binary cycle and procedures for cycle thermodynamic analysis focusing on the question of resource utilization are discussed. General and specific criteria for preliminary selection of working fluids and operating conditions for binary cycles are considered in terms of equipment and working fluid costs and in terms of resource utilization efficiency. Steps are given for preliminary binary cycle design computations. Preliminary evaluations of alternative pure working fluid, ideal thermodynamic cycles are illustrated. The development of the working fluid mixture thermodynamic cycle, GEO 1, using the improved versions of previously developed thermodynamic properties routines was the first of several significant accomplishments during the first half of this project. Documentation of the thermodynamic properties program which can calculate densities, enthalpies, entropies, heat capacities, K-values for vapor and liquid mixtures (limited presently to hydrocarbons), flashes, dew and bubble points, isentropic and isenthalpic state changes, has been completed. Preliminary calculations using GEO 1 have indicated that mixture cycles yield greater net power output than either pure propane, isobutane, or isopentane cycles when equal heat exchanger log mean temperature differencesmore » are considered and also when optimized ideal cycles are compared. Steps to upgrade GEO 1 with equipment sizing and economics routines to produce GEO 2 and GEO 3 simulators were begun.« less