In Spain, as in many other countries, the process of economic stagnation combined with a gradual aging of the population and an expansion of the level and extension of public pensions, has led many to argue that the pay-as-you-go system on which most public pension plans are based is unsustainable, and that it must be reformed to prevent its collapse. This study constitutes a contribution to the research Pensiones y prestaciones por desempleo (Pensions and Unemployment Benefits) (Fundación BBV, page 66), from the point of view of the possible inviability of the public pension system. It analyzes the degree of real cover provided by private pension plans, and the type of protection that would result from a system essentially depending on pensions managed by the private sector.