The performance increase for Heavy Duty (HD) gas turbines requires very high R&D efforts to improve life and reliability of the hot components. In fact the maximum temperature increase is the most important factor for the HD gas turbines development. Blade cooling of hottest and most loaded turbine stages becomes a fundamental key for R&D process in gas turbine design. Several innovations have been realised in last years about blade cooling and many industrial manufacturers have recently proposed new coolants, like steam or water. In this paper a detailed comparison among different cooling systems and coolants is proposed. Therefore performances of the most important HD gas turbine models are predicted and applications of the various cooling solutions are evaluated. An advanced cooling scheme based on air cooling closed loop is also studied. The simulations have been made from the point of view of blade cooling design and of global plant performances prediction. Interesting results have been obtained to confirm the present trend of R&D of HD gas turbines. Finally a wide comparison between different cooling solutions for several gas turbine models is presented.