The abnormally high rate of organic carbon deposition that occurred between 2.22 and 2.06 Ga contributed to one oft he most impressive accumulations of organic matter of its age, namely, the 2.1 Ga old FB Formation of the Franceville Series, Gabon. The weakly metamorphosed, dominantly pelitic FB Formation ranges in thickness from 400 m to 1000 m, covers more than 30,000 km(2), and consists of about 80% marine shale with 0.5-15% total organic carbon. About 2.0 Ga ago, the FB Formation generated prolific amounts of petroleum liquids. The coincidence of uranium-bearing aqueous solutions with the first and principal episode of liquid hydrocarbon migration led to the localization of world class uranium ores at Oklo. Relatively high-grade ore developed in petroleum-type structural traps, which ca. 1968 +/- 50 Ma served as loci for fifteen natural nuclear fission reactors at Oklo and nearby Bangombe. Hydrothermal solutions circulating about the reactors during their operation resulted in a second episode of local production/mobilization of liquid hydrocarbon. A third episode of hydrocarbon migration occurred during dolerite (diabase) dyke intrusion at Oklo ca. 977 to 971 Ma +/- 27 Ma ago. Altogether eight different types of carbonaceous substances (two kerogens, six solid bitumens) are identified in the black shales, uranium ores, and fossil reactors.