We report 66 new heat flow and 24 new heat production measurements from the Sirt Basin, a late Jurassic-Miocene sedimentary depression in north central Libya underlain by late Proterozoic basement. Heat flow determinations were made using bottom hole temperatures from oil wells and thermal conductivity measurements from drill core and cuttings; heat production measurements come from core samples of basement rock. Heat flow is fairly uniform throughout the basin, with a mean of 72¿9 (s.d.) mW m-2. It is not clear if heat flow from the Sirt Basin is elevated as a consequence of its origin as a late Mesozoic rift. The difference between the mean basin heat flow and the global mean heat flow from tectonically undisturbed late Proterozoic terrains (55¿17 mW m-2) is 17 mW m-2, but this difference lies within the uncertainties associated with these mean heat flow estimates. If heat flow from the Sirt Basin is elevated, it could be caused by enhanced crustal heat production and need not be attributed to thermal alteration of the lithosphere related to basin formation. Mean crustal heat production is 3.9¿2.1 μW m-3, 1/2 to 3 times greater than surface heat production in other Proterozoic terrains in Africa. From west to east, the pattern of heat flow across northern Africa is characterized by high (80--110 mW m-2) heat flow throughout most of northwestern Africa, normal to perhaps slightly elevated heat flow in the Sirt Basin, low to normal (35--55 mW m-2) heat flow in Egypt inboard of the Red Sea, and high heat (75--100 mW m-2) flow along the Red Sea. High heat flow near the Red Sea and in northwestern Africa along the Mediterranean coast can be readily attributed to Cenozoic tectonic activity, but high heat flow in the Paleozoic Sahara basins of southern Algeria is harder to understand within the tectonic framework of northern Africa. A possible explanation, advanced previously, is that elevated heat flow in the Sahara basins arises from a regional thermal anomaly within the north African lithosphere. If that explanation is correct, then the heat flow distribution in the Sirt Basin and in Egypt away from the Red Sea suggests that the postulated lithospheric thermal anomaly does not extend beyond the Sahara basins to the east. ¿ American Geophysical Union 1996