The creaming method of estimating undiscovered petroleum resources depends on modeling the petroleum explorer's ability to find the large fields early. There are, however, a number of other creaming phenomena evident in the exploration statistics for the Central Deep of the Gippsland basin. Consideration of these suggests a new method for estimating undiscovered petroleum resources and allows the limitations of the creaming methods to be examined. The new method gives results similar to the method. It involves simultaneous extrapolation of the predrill area of closure of the prospects and reserves per unit area, and it can be applied either to individual trap types or to all trap types within a region. In areas having a record of drilling but few discoveries, reserves per unit area can be determined from relationships among fields in a geologically similar region. Future success rates and the existence risk could be determined by geological risk analysis. The assessments probably underestimate the full potential of the Central Deep. Researchers should interpret them in the light of their limitations and of current knowledge of the region to determine the extent of the underestimation, and should see if there are any areas of significant potential that have been ignored. Any such areas could be assessed by other methods.