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Cross plot analysis of well log data and its calculated elastic atributes are one of the most effective methods to discriminate lithology and fluid type, because the geophysical rock properties analysis is relatively less time and cost compare to other method such as geological core sample analysis. This study uses well log data analysis based on cross plot, lithology separation, fluid type distribution map of 5 (five) wells at Nias Waters. The inverse of the interval transit times of the sonic logs are used to generate computed compresional velocities and Castagna-s formula for predicting S-wave data. Employing rock physics algorithms, rock properties including elastic attributes such as LambdaRho, MuRho, and Vp/Vs ratio are also extracted from the well log data. Cross plotting is carried out and plots with the most outstanding results are LambdaRho - Vp/Vs, MuRho - Vp/Vs, LambdaRho - Density, MuRho - Density, and AI - Vp/Vs. For the one well considered, the MT-1 well and its formation N10-N11 interest zone, those cross plots can identify lithology and fluid type. It determines formation N10-N11 as a gas carbonate reservoir with average porosity 23% which indicates that proper gas flow in the reservoir. Finally, the cross plot analysis are suitable to characterize reservoirs lithology and fluid type.