In accordance with an illustrative embodiment of the present invention, the state of the thermal maturity of organic matter extracted from a sedimentary rock sample is determined by using a microscope in combination with a color video camera to provide an image of the organic matter in transmitted and filtered light, using the output of the camera to compute RGB and HSB values for a selected area of the image on a per-pixel basis, and plotting values integrated over the selected area in the form of a thermal maturation pathway from which a likelihood that oil has been generated in the rock can be determined.