Method of controlling production of a plant incorporating one or more chemical processes in which products are produced through consumption of raw materials. In accordance with the method, current production rates of the products are computed by semi-empirical process models that are corrected through error corrections of actual production rates to produce corrected models. The production is then optimized using the corrected models to maximize the variable margin gained upon the sale of the products. The optimization yields targets that either directly or at least influence consumption of the raw materials. The raw materials are then introduced into the process or processes in accordance with the targets.