PRESTO (Probabilistic Resource ESTimates, OCS) is a computer program developed to provide resource estimates for offshore areas considered for leasing by the federal government. The program uses Monte Carlo simulation techniques to "drill" prospects that are geologically defined by the user, and then calculates resources using a volumetric formula. Resource estimates are given as probability distributions that reflect uncertainties in the physical representation of the prospects, rather than as single-point values or qualitative assessments. The program also incorporates a number of levels of geologic risk.

Four types of hydrocarbon resources are assessed for each reservoir: oil, associated and nonassociated gas, solution gas, and condensate. All are reported as distributions that can be converted and aggregated to a distribution for equivalent barrels of oil.

Unlike subjective resource estimation methodologies, the program provides reproducible results and can be used in frontier areas as well as mature producing basins. In addition, it provides an analysis of hydrocarbon potential at the zone and prospect levels, which can then be aggregated for basin and planning area estimates.

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