Maps of organic maturation in critical stratigraphic units, combined with organic-richness maps and kerogen identifications, provide the basis for a preliminary geochemical evaluation of the oil and gas potential of the Sverdrup Basin and the Franklinian Geosyncline in the Canadian Arctic Islands. Results of the study indicate that the main shale and siltstone units in the Islands have sufficient organic carbon content to be potential source rocks in one part or another of the archipelago. Maturation levels vary greatly, reaching extremes from immature to eometamorphosed not only in the Sverdrup Basin but also in the Franklinian Geosyncline. In the western Sverdrup Basin the following generalizations are noted: 1) Lower Cretaceous: immature (Ro < .5%) with potential for biogenic gas and locally some heavy condensates and oils; 2) Jurassic: moderately immature to mature (Ro. 5% to 1.2%) with gas and/or oil potential depending on basin position; 3) Triassic and Permo-Pennsylvanian: mature (Ro > 0.7%) with potential for oil and/or gas depending on area. Eometamorphic gas may be expected from the older sediments of this group in the deeper parts of the basin. Large parts of the eastern Sverdrup Basin are characterized by Ro values over 1 per cent in all units below the Cretaceous, reaching high levels with possible destruction of hydrocarbons in the Lower Triassic and older sediments. The Franklinian Geosyncline shows: 1) an area along its northern part in which the sediments have Ro levels between 0.5 and 2.0 per cent, approximately defining a favourable belt for oil generation; 2) an eometamorphic gas zone in the axial part of the geosyncline, where maturation levels exceed Ro 2.0 per cent; 3) in some areas maturation has reached Ro levels of 4.0 per cent with destruction of early oil accumulations, in some instances possibly reaching destruction of all hydrocarbons. While the archipelago is predominantly gas-prone, because of kerogen type in some cases or high maturation levels in others, oil may be expected in broad areas within both the Sverdrup Basin and the Franklinian Geosyncline. The Upper Triassic and Lower Devonian shales are believed to have been the sources of the largest volumes of hydrocarbons, predominantly gas in the former and oil in the latter. Table I summarizes the volumes of hydrocarbons estimated for the western part of the Sverdrup Basin. About 2100X10 12 cu ft of gas are estimated to have migrated to areas where reservoirs were present at one time, which could have trapped only a small fraction of this volume. Isotope analyses indicate that the gas in the seven large gas fields thus far discovered is of early thermal origin. Available information is insufficient to determine the parent rock of these gases and of the at least three types of oils found thus far in the Sverdrup Basin, or of the oil discovered recently in carbonates of Devonian age. It appears from limited data that the gas in the giant fields of Drake Point and Hecla had its source in Triassic rocks, whereas that of the fields in Ellef Ringnes and King Christian may have originated in the Savik shales. This study suggests that migration from the Mesozoic sources took place late in the basin history, probably not before late Early Cretaceous.