Any technique for estimating petroleum resources, no matter how detailed, should have a framework within which the data, concepts, and principles related to petroleum occurrence can be organized. The sedimentary basin is an entity that can be identified with a minimum amount of information early in the exploration history of a region, and that is capable of yielding a very tangible indication of hydrocarbon potential and its mode of occurrence.

There is no single ideal method of estimating resource potential. The method selected should be that best suited to the purpose of the study and to the technical resources and data bases available. Thus, for a worldwide assessment of resources including studies of unexplored regions or basins, one must select a method based on higher order characteristics before attempting any detailed approach.

In classifying the Phanerozoic Canadian basins for purposes of estimating petroleum resources, it was found that their evolution in both time and place was orderly relative to generally accepted principles of continental drift. There is clearly an evolution in basin styles through time, and there are corresponding, distinctive families of trapping configurations in each basin class.

The basin classification is placed in a chronogenetic framework through study of basin evolution in four major stratigraphic slices called "megasequences." An examination of giant oil and gas fields of the world within this basin classification framework demonstrates distinctive modes of occurrence in time (megasequence) and space (crustal position).