The basic pattern of heat flow in the Bering Sea is revealed by 43 measurements obtained in the Aleutian, Kamchatka, and Bowers basins. Averages of the observed values are 55 mW m-2 in the Aleutian Basin, 120 mW m-2 in the Kamchatka Basin, and 80 mW m-2 for two measurements in the Bowers Basin near the Bowers Ridge. Correcting these averages for the effects of sedimentation gives values of 69 mW m-2, 138 mW m-2, and 95 mW m-2, respectively. A useful nomogram for computing the thermal effect of an extended period of sedimentation is presented. Several methods of averaging heat flow values in marginal basins are compared using the data from the Aleutian Basin. If the Aleutian Basin was formed by the sea floor spreading process, then the heat flow suggests an age of about 44 m.y., which is considerably younger than magnetic data suggest. An alternative explanation is that the high heat flow is a residuum of thermal processes associated with the now extinct Kula Spreading Center and the Kula Plate, which underthrust the Bering Sea in the early Tertiary and thermally rejuvenated the trapped mesozoic sea floor underlying the Aleutian Basin. The high average jeat flow in the Kamchatka Basin suggests a considerably younger age for this basin, and the very high values in the southwestern part indicate either thin lithosphere or recent magnitic activity.