The expected changes in world reserves of conventional oil were interpreted in terms of the standard convention defining resources and reserves. According to this convention, oil is produced only from reserves which in turn are replenished only by discoveries. The change in reserves over one year is thus the sum of discoveries less the production for that year. The total discoveries were taken as the sum from two different sources: from those arising from the normal exploration process and from those that contribute to the Reserves Addition specified in the Year 2000 Assessment of the U.S. Geological Survey. These two quantities may change over time in opposite directions and it is this aspect that distinguishes this paper from previous studies.

The production projection taken from the previous underlying paper was based upon the Mean Value published in the Year 2000 Assessment of the U.S. Geological Survey. This paper also follows the earlier one in interpreting the Reserves Addition in two different ways that represent opposite boundary conditions. In Case 1, the Reserves Addition was only assumed active after the peak in production is passed and in Case 2, it was assumed to contribute to output through the whole production cycle. The actual situation is likely to lie between these two extremes. The changes in reserves were calculated year-by-year to 2050 for each case starting from values published in the literature for the end of 1999.

Despite this major difference in the underlying assumptions, the predicted fall in reserves over time was found to be virtually the same in both cases. Moreover, the peak in the rate of discovery per year was found to occur after the peak in production had passed although the Reserves-to-Production Ratio fell faster in Case 2. The major conclusion of this paper is that the published reserves should fall only slowly in the next decade. Changes in published reserves are thus not a good predictor of when the peak in world conventional production of oil may be expected. Nevertheless, considerations of self-consistency of the data require the reported value for reserves to start falling soon.