The new model for monthly average data is developed to predict monthly average global radiation with acceptable accuracy. The measured monthly average daily global solar radiation and sunshine duration for Istanbul-Samsun-Trabzon (Turkey), Varna (Bulgaria), and Odessa (Ukraine) were used to establish a second order polynomial equation for a suitable correlation model in Black Sea shoreline countries. Estimated data produced by the model were compared with the measured data. A good agreement between the estimated and the measured values of global solar radiation in Black Sea shoreline countries has been found. The new quadratic model seems to be used to estimate monthly average daily global solar radiation for the Black Sea region where the measured data is scarce.