Phelps Dodge Mining Company (Phelps Dodge) is operating a pressure-leach vessel (PLV) for copper concentrates at the Bagdad Mine facility in Arizona. This single PLV unit was engineered and constructed based on continuous laboratory testing, on reaction chemistry and kinetics and on available pressure-vessel technology. The challenge of designing for optimum process retention time, agitation, oxygen mass transfer, temperature and pressure are reviewed in this paper. The PLV interior lining, agitation equipment and compartment configuration chosen for the PLV are also reviewed.