Stratigraphic hydrocarbon fields are an important factor in the world's oil and gas production and reserves. Clastic stratigraphic traps occur primarily in basins, parts of basins, or sedimentary sequences characterized by tectonic instability and abrupt changes in lithologic facies. Reefs occur on stable shelves bordering troughs of deeper water sedimentation. Stratigraphic traps are most common in basins or parts of basins where large structural traps are scarce or absent. However, such occurrence should not be taken as a basis for concluding that hydrocarbons are preferentially trapped in structural closures. In fact, in many producing basins, oil and gas originally trapped stratigraphically have been remobilized after later structural growth to accumulate in anticline or fault closures. Most of the huge reserves of heavy oil in asphaltic sandstones in various parts of the world probably are the vestiges of oil accumulations that were trapped in stratigraphic wedges along the margins of basins; the oil has been lost by escape at the surface and evaporation of the light fractions.

Results of the application of modern exploration technology to the search for stratigraphic traps have been generally disappointing except in discovering carbonate reefs and banks. Detailed geophysical and geological studies have been successful in indicating areas of interest, but have not been precise enough to define the location of porosity wedgeouts within narrow limits. Nevertheless, a series of stratigraphic discoveries in North America in recent years demonstrates that large reserves of stratigraphically trapped oil and gas are being found even in basins that have reached a mature stage of exploration. Coordinated geological and geophysical studies for the prediction of favorable sourcerock, reservoir, and trap relations will bring rewards in exploration for stratigraphic as w ll as subtle structural traps.