The Paleozoic sedimentary successions in eastern Canada occur in four major tectonostratigraphic domains: the Lower–Middle Paleozoic autochthonous St. Lawrence Platform, extending from southern Quebec to western Newfoundland; the deformed Lower Paleozoic Humber Zone of the Appalachian orogen, located south and east of the St. Lawrence Platform; the Middle Paleozoic Gaspé Belt in eastern Quebec and northern New Brunswick; and the Upper Paleozoic Maritimes Basin in the Gulf of St. Lawrence and environs. Discovered oil and gas fields occur in Ordovician strata in the St. Lawrence Platform and external Humber Zone, Devonian strata in the northeastern Gaspé Belt, and Carboniferous strata in the Maritimes Basin.

Fifteen conventional petroleum plays are recognized in Paleozoic strata in eastern Canada. Six plays have sufficient exploration data to derive quantitative assessments of petroleum resource potential. The assessed plays include Lower Ordovician and Middle–Upper Ordovician hydrothermal dolomite plays in the St. Lawrence Platform, an Ordovician carbonate thrust-slice play in the external Humber Zone, a Lower Devonian sandstone play in the Gaspé Belt, and Mississippian and Upper Mississippian–Pennsylvanian sandstone plays in the Maritimes Basin. The cumulative median resource potential of the six assessed plays is 403 106m3 (2.5 billion barrels) of in-place oil and 1170 109m3 (41 Tcf) of in-place natural gas. The Maritimes Basin plays account for about 60% and 95% of the total oil and gas resource potential, respectively. The Upper Mississippian–Pennsylvanian sandstone play contains the largest predicted oil and gas fields in the region, with median volume estimates of 22.5 106m3 (141 million barrels) of in-place oil and 74 109m3 (2.6 Tcf) of in-place gas.

The assessment study provides important new insights into the petroleum resource endowment of Paleozoic basins in eastern Canada. In particular, the results indicate the Upper Paleozoic Maritimes Basin has a large conventional gas resource potential, much higher than previously estimated. The petroleum resource numbers represent a minimum for the region, because not all of the conventional plays were quantitatively assessed. The resource potential in the Cambrian–Devonian sedimentary successions may be much higher than indicated here.

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