Thin sections of 388 fine-grained rocks, which had been chemically analyzed for hydrocarbon content, were examined for details of lithology and paleontology. Three general types of thin-section observations were found to correlate with source-rock quality as determined chemically: (1) abundant visible organic matter, (2) dark-brown thin-section color, and (3) microlaminations (bedding < 1 mm thick). Of the clastic potential oil source rocks (> 500 ppm heavy hydrocarbon extractable) used in this study, 75% contain all 3 criteria. None of the nonoil-source rocks (< 150 ppm HC) have all 3 criteria. The "typical" potential oil source rock is described as "dark-brown, abundantly organic, microlaminated shale." This "typical" rock is commonly barren of fossils, but it ay contain a sparse benthonic fauna and (or) abundant pelagic microfossils concentrated in microlaminae. One set of depositional conditions able to produce this rock is a stable basin setting of relatively slow sedimentation, far from a major coarse clastic source, with no appreciable bottom currents, and with a low oxygen content at the sediment-water interface.

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