Data of chemical and isotopic cosiposition of fluids from Los Azufres geothermal wells is interpreted in order to characterize the composition of the liquid phase, and to define the relation between this phase and fluids from steam-producing wells. Chemical and specific enthalpy data show that most wells considered are fed a mixtureof steam and liquid. Thus, flashing occurs in the formation. This poses a problem on the interpret at i o n of is o topic data, because the composition of the feeding mixture need not be representa - t i v e of the composition of the liquid phase in the reservoir. Two extreme alternatives for the interpretation of is o to p i c data are considered. I n the first alternative the composition of the total discharge is considered to be the same as that of the liquid in the reservoir. In the second alter native the feeding fluid is con sidered to be a mixture of the liquid phase in the reservoir and the calculated fraction of steam. In addition, this steam is assumed to separate from a much larger mass of that liquid phase at the downhole temperature. The contri bution of steam is then substracted from the t: tal discharge to yield the composition of the liquid phase. Using data for silica concentr! t i o n in total discharge and separatedwater, the chloride concentration in there servoir liquid is calculated. This result is used to calcu - late the f r action of steam in the feeding mixt u r e of each well. The isotopic data is then corrected as proposed forth e secondalternative, to yield the composition of the liquid phase. Comparison of the corrected and uncorrected is? topic valuesshows that the correction has an important effect only when the steam mass fract i o n in the feeding mixture is large (> 20%). The correction tends to reduce the dispersion of data points in a 6 D vs 6"O diagram. Points representing composition of liquid phaseshowan approximately linear distribution, suggesting a process of mixing of two fluid s. Available data appears to rule out the possibility of mixture with local meteoric or shallow ground waters. Some spatial correlations of composition are no_ ted. The composition of fluids produced by two steam wells corresponds to steam separated from a much large r mass of liquid. Temporal variat ions in the composition of fluid produced by steam well A-6 suggests that t h i swell might be fed with steam from more than one section in the reservoir .

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