As complexity of exploration problems increases, petroleum geologists tend to consider more carefully oil formation and migration in terms of quantity, quality, and timing, in order to assess more accurately the history of hydrocarbons in a given basin. The present knowledge concerning the behavior of source rocks (quantity of hydrocarbons generated, composition of hydrocarbons, kinetics, expulsion efficiency) is that differences can be attributed to a large extent to organic properties of sediments, such as organic-matter content, organic-matter quality, and the pattern of the microdistribution of organic matter in the mineral fabric (layered, lenslike, intergranular). Moreover, field observations show that organic facies change at various scales in space and time, in re ponse to variation in depositional environments and sedimentary processes.

The effects of these factors on the source rocks emphasize, beyond the efforts to achieve comprehensive descriptions of source beds (Rock-Eval pyrolysis, microscopy, typing of organic matter, measurement of kinetic parameters of carefully selected kerogens, use of wireline logs, seismic information), the needs to increase our conceptual understanding of deposition of organic facies in order to improve our ability to predict the petroleum potential of sedimentary basins.