In refinery, fuel gas which is continuously generated during the production process is one of the most important energy sources. Optimal scheduling of fuel gas system helps the refinery to achieve energy cost reduction and cleaner production. A mixed integer linear programming (MILP) model for multi-period optimization of fuel gas scheduling is proposed in the paper. In this method, fuel gas is considered as the key energy source, while fuel oil and electricity as the secondary one. Site-wide fuel gas balance has been achieved by considering the storage ability of fuel gas system and the consumption of fuel gas both in cogeneration system and production system. The objective is to reach the minimum operation cost of the energy system by effective scheduling of the fuel gas system. Marginal value analysis, which provides additional economic information of the fuel gas system, is proposed in the paper. This analytical method is used to identify the system bottleneck and assist decision-making in the case study. (c) 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.