This report documents in detail the work performed by Westinghouse Electric Corporation and the Energy Research Corporation during the fourth phase of a planned multiphase program to develop a Phosphoric Acid Fuel Cell (PAFC) for electric utility or industrial power plant applications. Results of this effort include: (1) development of a baseline rolled electrode technology; (2) advancement of fuel cell technology through innovative improvements in the areas of acid management, catalyst selection, electrode and plate materials and processes, components designs, and quality assurance programs; (3) demonstration of improved fuel cell and stack performance and endurance; (4) successful scaleup of cell and stack design features into fun height 100 kill stacks; and (5) demonstration of combining stacks into a 400 kill module that will be the building block for power plants, including the development of testing facilities and operating procedures applicable to plant operations.