A study of electric power generating cycles which can be used in conjunction with a low-temperature geothermal energy (sensible heat) source is presented. Investigators at Los Alamos Scientific Laboratory have proposed a steam/isobutane dual cycle capable of generating 50.7 Mw of electric power. This cycle is optimized using regenerative feed water heating to yield a power output of 52.1 Mw or an improvement of 2.8%. Other power cycle designs and working fluids are investigated. Working fluids including various freons, steam, isobutane, ammonia, SO/sub 2/, CO/sub 2/, and several low molecular weight alkanes and alkenes are considered. The power cycle designs which are investigated include single and dual Rankine cycles (some of which involve regenerative feed heating), as well as topping/bottoming Rankine cycles, and Brayton gas cycles. The investigation shows that use of a single freon-11 cycle results in a 57.7 Mw power output representing an improvement of 13.8% over the LASL proposal. This cycle represents the best performance of all the combinations investigated, although several other cycles exhibit performance superior to that of the LASL proposal. It is recommended that the freon-11 single cycle be considered on an economic basis as a replacement for the steam/isobutane cycle in the proposed …