The figure below shows sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). The carbon-number distribution changes during pyrolysis, indicating a fundamental difference in composition between the immature extract and the kerogen. The pyrolyzate, however, is molecularly very similar to the oil.
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[[:file:oiloil-and-oilsource-rock-correlations_fig8-44.png|Figure 2]] shows sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). The carbon-number distribution changes during pyrolysis, indicating a fundamental difference in composition between the immature extract and the kerogen. The pyrolyzate, however, is molecularly very similar to the oil.