In multipurpose process plants, which are characterized by sharing different resources (equipment, manpower etc.) for production, unplanned equipment shutdown could affect the timely production of products and hence process profitability. Many approaches have been proposed to ensure high equipment availability by combining design, production, and scheduling frameworks with a maintenance optimization framework. In these approaches, the initial reliability characteristics of equipment, which also determine equipment availability, are considered fixed by problem definition. In this work, a combined design, production and maintenance planning formulation for multipurpose process plants is extended to incorporate the reliability allocation problem at the design stage. A simultaneous optimization framework is presented that addresses the problem of optimal allocation of reliability among equipment simultaneously with the selection of process configuration, production and maintenance planning for multipurpose process plants at the design stage. This framework provides the designer with the opportunity to select the initial reliability of equipment at the design stage by balancing the associated costs with its impact on the design and the availability in the operational stage. The overall problem is formulated as a mixed integer linear programming (MILP) model, and its applicability is demonstrated using a number of examples. (C) 2003 Elsevier Science Ltd. All rights reserved.