Oil shales contain organic matter from many sources, deposited under a variety of environmental conditions, which influence the potential for their commercial exploitation. Variations in organic matter type within the oil shales of the Lowmead Basin have been identified with reference to an integrated physico-chemical classification. The pyrolytic yield of the oil shales has been shown to correlate better with this classification than with a purely chemical classification. While the pyrolytic yield, in litres per metric tonne (l/mt), is satisfactory as a commercial assessment of the oil shales, the addition of TOC data is an additional indicator of the potential quantity and quality of the shale oil.