SPE Paper number 110765-MSTaken under conditions of uncertainty [1, 2]. Previous demonstrations of these biases, however, have focused on their impact on a single, typically technical, parameter judgment rather than examining their potential impact on economics when applied to all of the judgments involved in a complex Oil and Gas (O&G) decision such as reservoir characterization. Herein, we model the impact of three individual biases – overconfidence [2], bias resulting from the trust heuristic [3] and availability [4] - to measure their effect on economic outcome as represented by NPV. All three biases are shown to have marked effects on the estimated value of a project, not just its uncertainty. Overconfidence at the levels people common...