ABSTRACT Castro-Santos, L. and Diaz-Casas, V. 2015. Cost comparison of three floating offshore wind platforms. This paper proposes a method to calculate the total cost of a floating offshore wind farm. The method is based on the phases of the life cycle of such a farm. Each phase is defined by a cost, the value of which is either a constant or a variable parameter depending on the characteristics of a particular region. The tool so developed results in a georeferenced map of the total cost implied in the development of a floating offshore wind farm. Additionally, this method is applied to a floating offshore wind farm located in Galicia (in northwest Spain), as well as the three most important types of floating platforms: semisubmersible, tensioned leg, and spar. This paper is novel in that it helps to estimate the economics of floating offshore wind farms. In this sense, this study is one of the first of its kind to calculate the various costs associated with these types of wind farms.