This paper presents an actual FORTRAN program of probabilistic model for uncertainty analysis in estimating oil reserves. Factors in this calculation are expressed by triangular probability distribution and uniform random numbers are generated by multiplicative congruence method. The authors consider the shape effect of triangular distribution on estimation of oil reserves. Acknowledgment is given to Dr. Paul J. Root, Associate Professor of Petroleum and Geological Engineering, University of Oklahoma for his valuable informations concerning with Decisions under Uncertainty in carrying out this study.