The Southeastern Anatolia Project (GAP) of Turkey is a multi-faceted and integrated regional development project based on the concept of sustainable development. The project area covers nine provinces (Adiyaman, Batman, Diyarbakir, Gaziantep, Kilis, Mardin, Siirt, Sanliurfa and Sirnak) in the Euphrates-Tigris basins and Upper Mesopotamia plains. In this study, detailed weather data are presented for these provinces (except Sirnak). The data consist of new outdoor design conditions for heating and cooling according to the format recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. (ASHRAE), the heating and cooling degree-days for different base temperatures and the bin data for dry-bulb temperatures from -21 degreesC to 45 degreesC with 3 degreesC increments, in six daily 4-h shifts. These data are determined by using long-term recently-measured data. (C) 2003 Elsevier Ltd. All rights reserved.