May 12 (SeeNews) - BELEX15, the blue-chip index of the Belgrade Stock Exchange, closed higher for a fourth straight session on Monday, lifted by gains in civil engineering company Energoprojekt Holding [BEL:ENHL], insurer Dunav Osiguranje [BEL:DNOS], and Aerodrom Nikola Tesla [BEL:AERO], bourse data showed.