Plant layout is concerned with the spatial arrangement of processing equipment, storage vessels, and their interconnecting pipework. Deciding a good layout is an important activity in the design of chemical and process plants. A good layout will facilitate a correct operation of the plant. It will also provide an economic acceptable balance between the often conflicting constraints deriving; from safety, environment, construction, maintenance, operation, space for future expansion, and process relationships such as those determined by gravity now. This paper presents a mathematical formulation for addressing the problem of allocating items of equipment in a given two-or three-dimensional space. The objective function to be minimized is the total pumping, connection, and floor construction cost. Detailed cost factors are used to account for the flow direction between two connected units, The problem is formulated as st mixed integer linear programming model. Specific attention is paid to constructing a formulation which is; suitable for the solution of large scale problems. The method presents the rigorous solution of problems with about 30 process equipment and of essentially unlimited size problems when the rigorous optimization is combined with simple heuristic rules. Three case studies are presented to illustrate the applicability of the proposed approach to retrofit problems in multipurpose plants. Trade-offs between capital and operating costs are captured so that the optimal number of required moors maybe determined.