This article presents a probabilistic methodology for estimating the Net Present Value (NPV) of oil and gas production development projects. This methodology takes into account the uncertainties of important variables present in the economic evaluation, such as oil and gas production, prices, investments and operational costs. Furthermore, this paper aims to understand the impact of oil price change in the behavior of costs. It also presents a case study which allows indentifying and analyzing the results of the methodology implementation. The results show the importance of evaluating and quantifying the uncertainties in the economic appraisal, as well as the need to consider the effect of oil price changes. Hence, it points out an alternative to estimate the expect returns on investments according to a probabilistic approach, which can impact one of the most important variables for the economic project decision-making, the Net Present Value.