Extrapolating the discovery trend of the past to determine future discovery and production should be straightforward, and the size distribution of the fields should be evident. But the atrociously unreliable nature of public data has given much latitude when it comes to interpreting the status of depletion and the impact of economic and political factors on production. This has allowed two conflicting views of the subject to develop. The first is what may be called the Natural Science Approach, which observes the factors controlling oil accumulation in Nature and applies immutable physical laws to the process of depletion. The second is what may be called the Flat-Earth Approach, in which the resource is deemed to be virtually limitless, with extraction being treated as if it were controlled only by economic, political and technological factors. This paper will endeavor to present the evidence for the Natural Science Approach, addressing the geological constraints; the technical basis of reserve estimation; the distribution of field sizes; and the obvious correlation between discovery and production after a time lag. It will further explain the reporting practices, and present both a realistic assessment of the resource and a practical model of depletion.