In 1989, Chevron Overseas Petroleum, Inc., developed a process to allow management to compare a wide variety of global exploration opportunities on a uniform and consistent basis. Over the next five years, the process evolved into an effective method to plan exploration programs on a basis of value incorporating prospect ranking, budget allocation, and technology management. The final product is a continuous process and includes, within a single organizational unit, the integration of geologic risk assessment, probabilistic distribution of prospect hydrocarbon volumes, engineering development planning, and prospect economics. The process is based on the concepts of the play and hydrocarbon system. Other steps of the process (geologic risk assessment, volumetric estimation, engineering support, economic evaluation, and postdrill feedback) are considered extensions of fundamental knowledge and understanding of the underlying geological, engineering, and fiscal constraints imposed by these concepts. A foundation is set, describing the geologic framework and the prospect in terms of the play concept-source, reservoir, trap (including seal), and dynamics (timing/migration). The information and data from this description become the basis for subsquent steps in the process. Risk assessment assigns a probability of success to each of these four elements of the play concept, and multiplication of these probabilities yields the probability of geologic success. A well is considered a geologic success if a stabilized flow of hydrocarbons is obtained on test. Volumetric estimation expresses uncertainty in a distribution of possible hydrocarbon volumes for the prospect constructed from ranges of parameters obtained from information specific to the prospect, and data described by the parent play concept. With this distribution, engineering support provides development scenarios for three cases--a pessimistic case (10%), the mean, and an optimistic case (90%). Economic evaluation is run for each of the three cases, thus providing a range of economic consequences of the geological, engineering, and fiscal framework. Commercial risk is based on the results of this evaluation, and overall probability of success is the multiplication of the probability of geologic success and probability of commercial success. Postdrill feedback determines whether the individual processes are providing predicted results consistent with actual outcomes.