The chapter starts with the flow equations inside a U-oscillating water column. These equations are integrated numerically with the wave pressure β Δp(t) on the outer opening of the plant (Δp(t) is the wave pressure at a vertical breakwater, and β is a factor whose value is obtained with the solution of Chapter 15). The chapter resorts to design sea state and quasi-determinism theory for the Δp(t) aimed at estimating some extreme loads, and supplies a FORTRAN program for calculating this Δp(t). A worked example is given of an estimate of the maximum level reached by water and the extreme air pressure in the chamber. The production of electrical power is estimated for some slighter (and more frequent) sea states wherein Δp(t) is obtained through numerical simulation with a given spectrum. Estimates of productions are made for two hypotheses of Mediterranean plants and one hypothesis of oceanic plant.