The paper presents an optimization study for the mechanical and electrical equipment of an oscillating-water-column (OWC) wave power plant of fixed shoreline or nearshore type, equipped with an air turbine. The plant’s structure geometry is assumed to be given and the corresponding hydrodynamic coefficients are known as functions of wave frequency. A stochastic model is adopted for the energy conversion process from wave to air turbine, it being assumed that the system is linear. The optimization concerns the turbine size, represented by its rotor diameter D. Two alternative criteria are used: (i) maximization of the produced electrical energy, (ii) maximization of the annual profit. An example calculation is presented, based on the hydrodynamic coefficients of the OWC on the island of Pico, Azores, and on the aerodynamic performance curves of its Wells turbine. The influence of the following parameters upon optimized turbine size and rated power output is analyzed: wave climate, capital costs of mechanical and electrical equipment, operation and maintenance costs, discount rate, equipment lifetime and price of electrical energy supplied to the grid.