Decisions to invest in oil- and gasfield acquisitions or participating interests often are based on the perceived ability to enhance the economic value of the underlying asset. The realization of value, however, is a function of numerous outcomes that, in combination, may or may not meet economic expectations. Common industry evaluation practice entails estimating most likely reservoir results, development plans and costs, prices, and other factors within an economic framework. The risk of the opportunity is then assessed through sensitivities to key variables, such as rates and reserves or costs, often through multipliers, Such an approach fails to acknowledge explicitly the uncertainties of the project or integrate the variables so that they interact as a system. The lack of understanding of the project volatility becomes more critical when the deal structure is negotiable and could be used to reduce the economic volatility. A multidisciplinary approach integrating reservoir engineering, operations and drilling, and deal structuring with Monte Carlo simulation modeling can overcome weaknesses of deterministic analysis and significantly enhance investment decisions. This paper discusses the use of spreadsheets and Monte Carlo simulation to generate probabilistic outcomes for key technical and economic parameters for ultimate identification of the economic volatility and value of potential deal concepts for a significant opportunity. The approach differs from a simple risk analysis for an individual well by incorporating detailed, full-field simulations that vary the reservoir parameters, capital and operating cost assumptions,and schedules on timing in the framework of various deal structures.