The geological consensus is a useful method for estimating undiscovered oil and gas resources because the optimists balance the pessimists. Such group averages, however, are limited by the participants’ local expertise. Estimates of undiscovered oil and gas by petroleum geologists and engineers are much more conservative for areas where the experts have been humbled by dry holes and more optimistic wherever they have no direct experience. It is impossible to judge any expert’s degree of optimism or pessimism until his estimates are compared with those of a group of his peers. All group appraisals should be plotted on graphs, wherein each individual’s estimates are identified by a unique symbol to show the range of opinions. Estimates for virgin basins where no one has first-hand experience will normally be on the optimistic side.