Method for controlling the production of one or more liquid products produced by one or more plants, that can be an air separation plant, that has a liquid storage capacity and that consumes electrical power. Linguistic values related to current liquid inventory, a rate of change of liquid inventory, projected demand requirements and projected unit power costs are inputted into a expert system controller having one or more rule sets that apply such input linguistic values to produce output linguistic values that are converted back to an output numerical value of a forecasted differential production rate to be applied during a forecast period. The output numerical value of differential production is added to the current production rate of the plants to obtain a new production rate which is applied during the forecast period.