Abstarct: Calculation accuracy of petrophysical parameters and reduction of error determination of them is an important issue in the hydrocarbon reservoir studies. One of the main important factors to increase the calculation accuracy in petrophysical parameters is the measurement accuracy of well logging tools and low uncertainty in their results. The main purpose of this study is the determination of reservoir petrophysical parameters (especially permeability and water saturation) using Determin method, Monte-carlo analysis and probabilistic method and determination of those parameters uncertainties and generally petrophysical evaluation of the reservoir case study. In this study which is evaluated on Asmari formation located in one of the reservoirs in south-west of Iran, first the lithology of Asmari formation sequence were determined with neutron-density crossplot for wells A and B. Due to the mentioned method, calcite, dolomite, sandstone, shale and infrequent amount of anhydrite was observed in both wells. Then Determin method was used to calculate petrophysical parameters which conclude that well A has better reservoir conditions than well B. In the next step which is the main part of the study, the amounts of petrophysical logs uncertainties have been determined using Monte-carlo analysis. Afterwards by using logs uncertainties, petrophysical parameters in Asmari formation sequence were calculated using Monte-carlo analysis and proved, probable and possible values (1P, 2P and 3P) for each parameter in both wells were achieved. By the use of difference in these values, parameters uncertainties have been determined and the result shows that the highest uncertainty is for permeability and the lowest uncertainty relates to porosity. Lack of a log which could measure permeability directly, is the reason why this parameter has a high uncertainty and the reason why porosity has a low uncertainty, is due to the measurement of this parameter by using three porosity logs (neutron, density and sonic). Also the uncertainty in top of the both wells that have carbonate-dominated lithology is greater than sandstone-dominated lithology in the bottom parts of the wells. The reason is due to the complexity of porosity and permeability systems in carbonate reservoirs in respect to sandstone reservoirs. Also by using the petrophysical tornado charts, sensitivity analysis has been done and the effects of these parameters and logs on equivalent hydrocarbon column (EHC) have been studied. The results show that the neutron log has greatest impact on EHC factor in both wells.