A new heat flow map has been constructed for northeastern British Columbia, using log-heading temperature records corrected for drilling disturbance, at depths ranging from 200 m to over 4000 m. Geothermal gradient varies from 20 to 90 mK/m (degrees C/km). A significant regional trend of southward and southwestward decrease of geothermal gradient is observed in the map area. Effective thermal conductivity, based on an analysis of an evenly distributed network of wells throughout the area, shows variation in the range 1.2 to 2.4 W/mK. Very large variations of terrestrial heat flow, from 40 to 130 mW/m(2), suggest a large imprint of highly variable heat generation in the upper crust. The lowest heat flow is observed in the southern part of the study area and especially in the southwest. The highest heat flow is in the north, with values commonly exceeding 100 mW/m(2). However, lower heat flow values (< 60 mW/(2)) are also observed in the north. In the deep western part of the basin, low beat flow in the south contrasts with high heat flow north of 59 degrees N. Reduced (deep) heat flow in the north is probably 10 to 20 mW/m(2) higher than the average of 33 mW/m(2) proposed previously. Higher regional reduced heat flow and higher than average heat generation (2-4 mu W/m(3)) of the basement rocks likely accounts for part of the northern high heat flow. It is estimated that the average temperature at a depth of 5 km is 180 degrees C; however, temperatures as high as 140 degrees C are recorded at the much shallower depth of 2 km in the northern and northeastern part of the study area.