The optical studies of fossil organic matter in reflected light have made great progress in recent decades with the development of coal petrology, completed around the end of the 1970s by fluorescence examination. As they are complementary to the studies in transmitted light (palynology) and organic geochemistry developed for petroleum exploration purposes, they have become a much used tool in the recognition of sedimentary thermal transformations. For more than fifteen years within the Elf-Aquitaine Group, these studies have been applied in their various aspects to furnish a better...