A modular GASP IV model of a chemical plant and its use in analyzing the operation of the plant is described. The model represents multiple stages and products and was developed to evaluate methods for increasing throughput. The plant manufactures six products, each going through a series of steps; different products can be in production at the same time. The paper also includes the data-collection procedures and the evaluation of several alternatives proposed to increase the throughput of the plant by as much as 100%.