The number, sizes, and temporal trends of hydrocarbon discoveries can be used to project the remaining potential for a basin or area of interest. This paper describes a simple graphical method for projecting number and size of potential future discoveries. The graphical approach enables adjustments for geological characterization, exploration maturity, and basin complexity. The method requires enough discoveries to define the presumed parent population on a log-log plot of discovery size versus size rank. A breakpoint separates the presumed parent population from the undersampled part of the distribution. Potential breakpoints can be identified by comparing an interval slope above and below each discovery.

Larger discoveries are typically made early in the exploration process. Plots of cumulative discovered volume versus discovery number illustrate this effect through progressive flattening. Although the creaming effect is well established, basins can differ in this regard. We introduce a measure of basin complexity such that in higher-complexity basins some larger discoveries are made later. Accounting for basin complexity is essential for projection of future potential. Some basins contain outlier fields that are larger than expected based on the parent population (also known as king fields), and these too must be accounted for by the projection method.

Discovered fields for a basin typically approximate a lognormal distribution, likely a result of sampling bias in the exploration process. To mimic this pattern, a subset of smaller fields is excluded from the predicted future discoveries using an approach linked to the presumed economic minimum.