The fluorescence alteration of multiple macerals (FAMM) technique was introduced for the thermal maturity assessment of dispersed organic matter (DOM) in rocks, and it is calibrated in equivalent vitrinite reflectance (EqVR) against Australian Permian coals. In this study the technique has been tested on North American Carboniferous, Late Cretaceous and Early Tertiary coal and other rock samples on which VR measurements had previously been made. Rock-Eval hydrogen index (HI) and FAMM data indicate that the composition of most of the coals does not deviate greatly from ＇normal＇, but some of the vitrinites tend toward perhydrous or subhydrous composition. FAMM EqVR and measured VR values are well correlated but the correlation improves if FAMM-derived corrections for suppression or enhancement are applied to the VR values. Comparison of the FAMM and VR results on samples from two wells penetrating late Mesozoic and Cenozoic coal seams and shales shows that VR trendlines for the different lithologies are displaced whereas EqVR trends are more consistent. For both wells there is a slight but significant difference between the measured and equivalent VR trends which may be related to the fact that errors of the order of 0.1%R(o) absolute are possible near the limits of the range of the FAMM technique (VR = 0.4-1.2%R(o)).