Middle Jurassic coals from Kuhn empty set, North-East Greenland, may contain up to 85 vol.% liptinite, principally resinite (up to 68.6 vol.%), The coals are thus petrographically comparable to the Middle Jurassic Muslingebjerg Formation coals at Hochstetter Forland approximately 40-50 km to the north, and they are inherently excellent petroleum source rocks. Liptinite-poor(less than or equal to 6.0 vol.%) coal samples from both Kuhn empty set and Hochstetter Forland yield mean random huminite reflectance values of 0.49-0.53% R-o, implying a rank of sub-bituminous A. Above a threshold value somewhere between 3 and 24 vol.% resinite and 6 and 35 vol.% total Liptinite, significant reflectance suppression is induced, and between 24 and 69 vol.% resinite and 35 and 85 vol.% total liptinite, a nearly linear inverse relationship exists between the content of liptinite/resinite and the mean random reflectance values. At the highest liptinite/resinite contents, reflectance suppression may be up to 0.23%R-o. The reflectance suppression is related to bitumen-adsorption caused by bitumen-expulsion from resinite, and total reflectance distributions of the huminite fractions suggest that the reflectance of all huminite macerals is lowered with increasing Liptinite/resinite content.