Bottom-hole temperatures were measured in groundwater observation wells in the Athabasca Oil Sands area of Alberta. Depth of observation varies from 6–581 m in rocks of Holocene, Cretaceous, and Devonian age. Observations of temperature at various depths at a particular location were made in individual wells.At depths of 300 and 400 m, a correlation of both hydraulic head-loss and temperature with the elevation of the land surface at the observation well indicates that groundwater flow is the dominant parameter controlling subsurface temperatures. The control of groundwater flow on temperature and the location of observation wells in different positions in the groundwater flow system means that temperatures are not well correlated with depth.Bottom-hole temperatures from geophysical logs made in the area are significantly higher than values observed nearby at similar depths during this study. Published thermal gradient maps based upon information from geophysical logs give values which are about twice as high as those calculated with the present data.At depths less than about 60 m temperatures varied widely and at many well sites declined with depth. The average temperature of shallow groundwater was 5.9 °C at an average depth of 12.7 m. This fact indicated that the mean annual air temperature of −0.6 °C should not be used to approximate the temperature of shallow groundwater.