Book excerpt: Presented in this publication are the results of a major study of the petroleum resources of the world as analyzed by Total Petroleum Systems. The distribution and volumes of resources available in these systems are critically important for the future of the world's economies. Geologic insights gained from studying these 149 systems and their constituent assessment units in 128 provinces and 96 countries, exclusive of the United States, allow a new look at petroleum accumulations and the rocks that are intimately associated with them.