A recent USGS open file report entitled Ranking of the World's Oil and Gas Provinces by Known Petroleum Volumes groups the worlds 937 geologic provinces into eight regions by known petroleum volumes of field. This site succintly describes the ranking methods used and results of the study. Perhaps not surprisingly, the Middle East and North Africa was found to contain nearly twice as many billions of barrels of oil than any other area. The researchers hope that the rankings will "facilitate studies of reserve growth, assessment of undiscovered resources, and analysis of economics and risk".