The Middle Devonian Winnipegosis Formation and the Upper Devonian to Lower Mississippian Bakken Formation in southeastern Saskatchewan have been studied to assess their thermal maturity levels with respect to petroleum generation. Fluorescent and white incident light microscopy has been used to determine vitrinite reflectance in oil (%Ro) and maximum wavelength fluorescence emissions (lambda max) for alginite macerals in the two formations. Vitrinite reflectance for the Winnipegosis Formation ranges from 0.33 to 0.86 %Ro. A reflectance-depth profile indicates that a low and a high paleogeothermal gradient probably affected Winnipegosis strata in the region of study. Peak hydrocarbon generation for Type II kerogen source rocks in the Winnipegosis Formation is marked by a vitrinite reflectance of near 0.70 %Ro and by a red shift in alginite lambda max values toward longer wavelengths (> 570 nm). Thermal maturity levels of the Bakken Formation range from immature to marginally mature (0.30 to 0.68 %Ro). Based on vitrinite reflectance and alginite lambda max values, a relatively low and a relatively high paleogeothermal gradient also seems to have affected the Bakken Formation shales. A low maturation gradient is proposed for western borehole locations whereas the higher gradient is proposed for eastern borehole locations. Minor hydrocarbon generation has occurred in the western portion of the study area where radioactive-element decay from phosphatic particles has stimulated ＇＇microscopic＇＇ thermal anomalies and more extensive bitumen formation.