The rank of coal in the Eureka Sound Formation on Ellesmere and Axel Heiberg Islands ranges from brown coal to high volatile bituminous coal, based on reflectance determinations. Reflectance values from coals adjacent to the Stolz Fault, Axel Heiberg Island, are higher than in adjacent areas and may be related to abnormally high heat flows resulting from evaporite diapirism at depth, from the effect of overthrusting, or both. Regional reflectance values indicate that there is no correlation between the degree of coalification and the age of the strata, suggesting differing depths of burial and tectonic settings. Comparison of the coalification gradient at Fosheim Peninsula, Ellesmere Island, with that of the Téjon area of California permits estimation of a geothermal gradient which can be used for calculation of preorogenic sediment thickness. Maximum temperatures derived from the degree of coalification (100 °C at Fosheim) suggest that the sediments are within the zone of initial oil maturity.