The Mesozoic Bowser and Sustut basins occupy more than 60,000 km2 of the Intermontane Belt of the Canadian Cordillera. Both are deformed in the thin-skinned Skeena Fold Belt that terminates in a triangle zone. Petroleum resource potentials of these basins must be re-assessed using new stratigraphic and tectonic models which consider the physical environment, primarily temperature, and temporal relationships among hydrocarbon generation, migration, entrapment, and preservation. The first widespread thermal maturity data set for the Bowser and Sustut basins illustrates that large regions have sufficiently low organic maturity levels that both the generation and preservation of hydrocarbons and the diagenetic history of reservoirs is favourable for the formation and preservation of a significant petroleum resource. This result is a substantial change from previous views that considered the high thermal maturity of some of the highest Bowser strata as a negative indication for hydrocarbon potential in all stratigraphic levels of all regions of the basin. Although parts of the study area are at very high thermal maturity levels, there are clear regional variations in the thermal maturity of outcrops such that even the lowest stratigraphic units are marginally to fully mature in select regions of the basin.