An estimated monthly average of daily diffuse solar radiation on horizontal surfaces for a total of sixteen meteorological stations in Libya has been computed using the correlations of Iqbal (1979), Page (1964), Collares-Pereira and Rabl (1979), and Erbs et al. (1982). The data of bright sunshine hours and global solar radiation was obtained from fifteen of the meteorological stations during the period between 1981 and 1987. Data from the remaining station, at Tripoli airport, was obtained during the period between 1961 and 1990, and at only this location were true diffuse radiation measurements recorded. This measured data from Tripoli airport was then compared with the correlations of Iqbal (1979), Page (1964), and Collares-Pereira and Rabl (1979). Excellent agreement was found between the correlation of Collares-Pereira and Rabl (1979) and the measured data.