Concerning the problems of oil field development, if models are adequate substitutes of actual systems under consideration, many kinds of properties and optimum solution of actual systems may be obtained through simulation techniques. The authors present here a techno-economical appraisal method of projects on off-shore oil field development using a simulation model included a probability model for uncertainty analysis in estimating oil reserves. Aims of this method is to create a probability distribution of expectable cash flow, using a distribution of oil reserves as a basis, and to analyze probability problems. For these aims, cost of exploration, wild cat, platform, production facilities and others must be evaluated, and production scheme and the tax system for each country must be studied. Simulation models must contain all these factors. This technique yields a probability distribution of cash flow in monetary values, which is useful as an economic yardstick. It is possible to evaluate a total risk capital, a fractional participation and a value of new informations that decrease the probability of failure. If model is satisfactory with good precision, it is also possible to find the optimum production scheme among many trial runs of calculation. The computer HITAC 8800 spends 17 seconds for a set of calculations with the model used in the example case.