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This paper discusses an approach to determining the least-squares optimum order of a polynomial fit to temperature-gradient data. The optimum is reached when two successive least-squares regional maps are sufficiently similar. This similarity is measured by the correlation factor between the polynomials.

The approach was applied to the available deep bore-hole temperature data in the central part of the Northern Western Desert of Egypt. The fitting polynomial was found to be of the second degree. Assuming the thermal conductivity to be uniformly 2.2 Wm(-1)K(-1) for the stratigraphic section in the Western Desert, the heat-flow density ranges between 35 and 70 mW/m(2).