A new report published on March 10 by a team of researchers from the University of Oxford, based on the largest ever study of large hydroelectric dams (245 in 65 countries) has found that in most cases large dams are economically not viable and few, if any, will realise their planned benefits. The study assessed the costs, construction time, and benefits of all large dams built around the world since 1934, and further concluded that the severe cost and construction delays that so often dog large dams (defined in this research as those that exceed 15 metres in height) mean they can be seriously damaging to the economies that attach so much hope to them.